Bitcoin Basics

The History of Money (Why This Matters)

To understand Bitcoin, you first have to understand money — specifically, what goes wrong with it.

For most of human history, money was something physical. Gold. Silver. Shells. Things you could hold, that were scarce, that couldn’t just be conjured out of thin air. If you had gold, you had value. Nobody could print more of it.

Then we moved to paper money — and paper money started out as a receipt. You hand over your gold, the bank gives you a piece of paper saying ‘we owe you this gold.’ Convenient. Fine.

But over time, something shifted. Governments and banks started printing more receipts than they had gold to back them. In 1971, the United States formally disconnected the dollar from gold entirely. From that moment on, the dollar — and every major currency in the world — became what’s called fiat money. It’s worth something because the government says it is. Not because it’s backed by anything real.

And the consequence of that? Inflation. The purchasing power of your savings erodes, year after year, because more money is constantly being created. The people at the top of the system benefit. Everyone else slowly loses.

Bitcoin was built as the answer to that problem.

Satoshi Nakamoto and the 2008 Whitepaper

In October 2008, right in the middle of the worst financial crisis in living memory — banks collapsing, governments bailing them out with freshly printed money — a person using the name Satoshi Nakamoto published a nine-page document called ‘Bitcoin: A Peer-to-Peer Electronic Cash System.’

We don’t know who Satoshi is. Could be one person, could be a group. They disappeared from the internet in 2011 and have never been identified. And that anonymity — as we’ll see later in this course — turns out to be one of Bitcoin’s most important features.

But the idea in that whitepaper was radical. Satoshi proposed a form of digital money that didn’t require a bank, a government, or any company to operate. A system where you could send value to anyone in the world, directly, without asking anyone’s permission.

No middleman. No third party. No one who could freeze your account, reverse your transaction, or print more of it to devalue what you already held.

That’s the idea. Now let’s look at how it actually works.

Trust vs. Trustless Systems

Every financial system in the world today is built on trust. You trust your bank to hold your money. You trust your government not to inflate it away. You trust the payment processor when you swipe your card. You trust a dozen different companies and institutions every single day just to use your own money.

And most of the time, that trust holds. But sometimes it doesn’t. Banks fail. Governments freeze accounts. Payment processors block transactions for political reasons. In some countries, people wake up one morning and their savings have been seized or inflated into worthlessness overnight. This isn’t hypothetical — it has happened, repeatedly, across history.

Bitcoin replaces trust with mathematics.

Instead of relying on a bank to keep a ledger of who owns what, Bitcoin uses a public ledger called the blockchain — a record of every transaction ever made, stored simultaneously on thousands of computers all over the world. Nobody owns it. Nobody controls it. And everyone can verify it independently.

To change the history on this ledger, you would have to redo an enormous amount of computational work — work that would cost more money than it’s worth to attack. The system is secured not by laws, not by guards, but by mathematics and energy.

When we say Bitcoin is ‘trustless,’ we don’t mean you blindly trust nothing. We mean you don’t have to trust any specific person or institution. You can verify everything yourself.

Bitcoin vs. Banks: Who Controls Your Money?

Here’s a question worth sitting with: do you actually own the money in your bank account?

Legally? Not exactly. When you deposit money in a bank, you become an unsecured creditor of that bank. They owe you the money — but they’re also lending most of it out, investing it, and using it as they see fit. You have a claim on it. That’s not the same as owning it.

Your bank can freeze your account. They can block certain transactions. They can be forced by a government to hand over your funds. They can go insolvent. These aren’t paranoid fantasies — they’re things that happen.

Bitcoin works differently. When you hold Bitcoin properly — meaning you hold the private keys yourself, which is what this entire course is about — nobody can freeze it, seize it, or block you from using it. There is no customer service line to call and no account to close. The Bitcoin simply exists on the network, and you control it with a cryptographic key that only you possess.

Now, that power comes with responsibility. And that’s exactly why this course exists. Self-custody — the act of truly owning your Bitcoin — requires knowledge. It requires the right setup. And it requires the security habits we’re going to build together over the coming modules.

What a Block Is and What It Contains

Let’s start with the word itself. Blockchain. Take it apart: you have blocks, and they form a chain. A block is simply a batch of Bitcoin transactions — like a single page in a ledger. Every ten minutes or so, the Bitcoin network collects all the recent transactions people have broadcast, bundles them together, and seals them into a new block.

Each block contains roughly two thousand transactions on average, a timestamp recording when it was created, and something critical: a digital fingerprint of the block that came before it. That fingerprint is called a hash. Think of it like a wax seal on an old letter — the seal proves the letter hasn’t been opened. But a hash is even better than a wax seal, because any change to the contents — even a single character — produces a completely different fingerprint. It’s as if tampering with one word in the letter would cause the seal to visibly shatter.

So when Block 2 contains the hash of Block 1, it is permanently linked to it. If anyone tried to alter Block 1 — even changing a single transaction — its hash would change entirely, and Block 2’s reference would no longer match. The chain breaks. Imagine a row of dominoes where each domino is engraved with a description of the one behind it. If you swap out a domino in the middle, every engraving after it becomes wrong — and everyone can see it. This is why the blockchain is immutable: every block is cryptographically locked to the one before it, all the way back to the very first block — the Genesis Block — mined by Satoshi in January 2009.

Proof of Work: How Miners Compete to Add Blocks

Here is where it gets interesting — and where most explanations start losing people. Who decides which transactions go into each block? And who actually adds the block to the chain? The answer is miners. And they earn the right to add a block through a process called Proof of Work.

Here is the simplest way to explain it. Imagine a combination lock with trillions of possible combinations, and the only way to open it is to try one combination after another, as fast as you possibly can. There is no shortcut. No clever trick that skips ahead. Just raw, repeated computational effort. Miners are doing something mathematically equivalent. They race to find a number — called a nonce — that, combined with the block’s data, produces a hash meeting the network’s specific requirements. The first miner to find it wins.

The winning miner broadcasts the new block to the entire network. Every other node independently verifies that the transactions are valid and the Proof of Work is correct, then adds it to their copy of the blockchain. The winner receives two things: newly created Bitcoin called the block subsidy, and every transaction fee included in that block. Think of miners like gold prospectors — they invest real resources (electricity and hardware) in exchange for the chance to find something valuable. This is the only way new Bitcoin enters circulation — not printed by a central authority, but earned through verifiable, expendable work.

Why the Longest Chain Wins

Here is a question you might be wondering about: what happens if two miners find a valid block at almost exactly the same moment? For a brief period, there are two competing versions of the blockchain. The network temporarily splits. This is where one of Bitcoin’s most elegant rules resolves everything: the longest chain wins. Not longest by number of blocks — by accumulated Proof of Work. The chain with the most total computational effort behind it is the canonical chain.

When nodes detect a competing chain that has accumulated more Proof of Work, they switch to it automatically. The shorter chain’s blocks become orphaned — technically valid but not part of the main chain. Any transactions in those orphaned blocks simply re-enter the mempool and get picked up in future blocks. The conflict resolves itself, without any central authority making a call.

This is also what makes Bitcoin extraordinarily resistant to attack. To rewrite any part of the blockchain — to reverse a confirmed transaction — you would need to redo all the Proof of Work from that point forward, faster than the rest of the network is building ahead. Imagine trying to rewrite every page in a library book while the library is simultaneously adding new pages faster than you can write — it is a race you simply cannot win. With Bitcoin’s current hash rate, executing such an attack would require more computing power than exists on Earth. It is not merely difficult. It is economically irrational.

Confirmations and Transaction Finality

When you broadcast a Bitcoin transaction, it first lands in what is called the mempool — short for ‘memory pool.’ Think of it as a post office lobby where letters are waiting to be sorted and dispatched. Your transaction sits there, visible to the network, until a miner picks it up and includes it in a block. It is a waiting room of unconfirmed transactions. Miners select transactions from the mempool when assembling their next block. Once your transaction is included in a mined block, it has one confirmation. Think of each confirmation as a new layer of mathematical cement poured on top of your transaction.

Each additional block added to the chain after yours is one more confirmation. Every confirmation makes it exponentially harder to reverse that transaction, because an attacker would need to redo the work for your block and every block stacked on top of it. Six confirmations is the widely accepted standard for considering a transaction final. At current block times, that is roughly one hour.

For small everyday payments, one or two confirmations is typically sufficient. For significant transactions — a large purchase, a major transfer — waiting for six or more is standard practice. The higher the value at stake, the more confirmations you should require before treating it as settled.

Private Keys: What They Are, Why They Are Everything

A private key is a number. Specifically, it is a 256-bit number. If that sounds technical, here’s what it means in practical terms: the number of possible private keys is so astronomically large that if every atom in the observable universe were a computer trying combinations, they could not guess yours in the lifetime of the universe. Your private key is generated randomly when you create a Bitcoin wallet. Nobody else has it. Nobody can derive it. It exists only where you have stored it.

This number — this key — is your proof of ownership. When you want to send Bitcoin, your wallet uses your private key to create what’s called a cryptographic signature. Think of it like signing a check — except this signature mathematically proves that only the holder of the private key could have authorised the transaction, without ever revealing the key itself. The Bitcoin network verifies the signature and processes the transaction. No bank authorises it. No company approves it. The key is the authority. And this is why the phrase “not your keys, not your coins” is not just a slogan — it is a literal technical fact. If someone else holds your private key, they own your Bitcoin.

When you hold Bitcoin on an exchange, the exchange holds the private keys. You have a number in a database that says how much Bitcoin they owe you. That is not the same thing as holding Bitcoin. As the industry learned from Mt. Gox, from FTX, from Celsius, and from dozens of others — if the exchange fails, freezes, or simply decides to stop operating, your access to that number disappears with it. Self-custody means you hold the key. Nobody can take your Bitcoin unless they take your key.

Public Keys and Bitcoin Addresses

Your private key never travels anywhere. But Bitcoin needs a way to receive funds — a destination address you can share publicly. Here is how that works. From your private key, your wallet performs a series of one-way mathematical operations to produce first a public key, and then a Bitcoin address. The technical names for these operations — elliptic curve multiplication, SHA-256 hashing — are not important to memorise. What matters is one simple concept: these operations are like a one-way door. You can walk from private key to address, but you cannot walk back. Nobody can take your Bitcoin address and work backwards to figure out your private key. It is mathematically impossible.

Your Bitcoin address is what you share when someone wants to pay you. Think of it like the address on your mailbox — anyone can send you a letter if they know the address, but knowing the address doesn’t give them a key to get inside your house. Sharing your Bitcoin address with the world does not put you at risk. Nobody can extract your private key from your address. You can publish your Bitcoin address openly. You can print it on a business card. You can post it online. None of that endangers your funds. What endangers your funds is exposing your private key — or your seed phrase, which we will cover next.

One more important detail, and it’s one that trips up almost every beginner: never reuse a Bitcoin address. Modern Bitcoin wallets generate a new address for every transaction. This is not a bug or an inconvenience — it is one of the most important privacy and security features your wallet provides.

Here’s why. The Bitcoin blockchain is a permanent public record. Every transaction ever made is visible to anyone who looks. When you reuse an address, you create a single thread that ties all of your transactions together. Anyone — a curious neighbour, a chain analysis company, a government agency, a criminal — can type that address into a block explorer and instantly see every payment you’ve ever received and every payment you’ve ever sent from it. Your balance, your spending habits, your counterparties — all of it, laid bare.

Think of it like this: imagine you had a single mailbox that you used for every piece of mail in your life — your pay stubs, your medical records, your love letters, your tax returns. Now imagine that mailbox was made of glass and sat on a public sidewalk. Anyone walking by could see everything inside. That’s what address reuse does to your financial history on the blockchain. A new address for each transaction is like using a different P.O. box for each category of your life — no one can connect them unless you tell them to.

The good news: your wallet handles this automatically. Every time someone sends you Bitcoin, your wallet provides a fresh address. You don’t have to think about it or manage it manually. Just make sure you never go out of your way to share the same address twice — for instance, don’t post a single Bitcoin address on a website or social media profile and reuse it for all donations. We’ll go much deeper into why this matters in Module 5 when we cover chain analysis and privacy strategies, but the habit starts now: one address, one use.

The Seed Phrase: Your Master Backup

Here is the problem with private keys: a raw 256-bit private key is a long string of random characters. No human can memorise that or safely write it down by hand. So the Bitcoin community developed a clever solution: a way to encode that key as a sequence of 12 or 24 ordinary English words. This is your seed phrase. Think of it as a human-readable translation of your key — like translating a complex equation into plain English so you can write it on a notecard and lock it in a safe. Your wallet generates it when you set up a new wallet, and you must write it down immediately on paper, in order, and store it somewhere physically secure.

This is the most important thing I will tell you in this entire lesson. Your seed phrase is your master key. Every private key your wallet will ever generate — every address, every transaction, every coin — can be derived from that seed phrase. Which means that whoever has your seed phrase has your Bitcoin. All of it. There is no reset button, no customer service line, no recovery process. If someone photographs your seed phrase, they can drain your wallet. If you lose your seed phrase and your hardware wallet breaks, your Bitcoin is gone forever.

Write your seed phrase on paper — never type it into any device, never photograph it, never store it digitally in any form. For serious holdings, consider stamping or engraving it onto a steel plate. Products like Cryptosteel, Blockplate, and SeedPlate are designed specifically for this. They survive fire, water, and decades of time. Your seed phrase needs to outlast every digital device you own. Paper is a reasonable start. Steel is the standard. We cover backup strategies in detail in Module 4.

HD Wallets and Derivation Paths

One seed phrase, thousands of addresses. How? This is the purpose of what are called HD wallets — Hierarchical Deterministic wallets. Don’t worry about the name. Here is the simple version: imagine a master key that can cut an unlimited number of unique house keys, and each house key opens a different door. Your seed phrase is that master key. Every time your wallet generates a new receive address for you, it is cutting a new house key from that same master. This is the standard used by virtually every modern Bitcoin wallet.

What this means in practice is remarkable: your seed phrase is your entire wallet, forever, on any device. If your hardware wallet fails tomorrow, you buy a new one, enter your seed phrase, and your wallet is completely restored — every address, every transaction history, every balance. This is not a feature of the device. It is a feature of the mathematical relationship between your seed phrase and every key it can generate. The device is just a tool. The seed phrase is the wallet.

You may encounter the phrase ‘derivation path’ — notation that looks like a string of numbers and slashes. Don’t let it intimidate you. Think of it as an address inside a filing cabinet: it tells the wallet software which drawer to open, which folder to look in, and which document to pull out. Different wallet types use different filing systems, which is why it is important to note which type of wallet you created — Legacy, SegWit, or Native SegWit — when you back up your seed phrase. Your wallet software handles all of this automatically; you do not need to memorise any of it. But if you ever need to recover your wallet in an unfamiliar application, knowing the derivation path ensures you find all your funds.

Anatomy of a Bitcoin Transaction

Every Bitcoin transaction has the same basic anatomy: inputs and outputs. Inputs are the funds you’re spending — they point back to previous transactions where Bitcoin was sent to you. Outputs are where the Bitcoin goes next — either to the recipient or back to yourself as change. Think of it like using a $50 bill to pay a $30 tab. You hand over the $50 as the input. The restaurant takes $30 as one output. You receive $20 in change as a second output. Bitcoin works exactly the same way, except it all happens cryptographically on a public ledger.

Here’s how a real transaction looks: someone wants to send 0.1 BTC. Their wallet finds a previous output — let’s say 0.15 BTC — that was sent to their address. It creates a new transaction with two outputs: 0.1 BTC to the recipient’s address, and 0.049 BTC back to a change address the sender’s own wallet controls. The difference — 0.001 BTC — goes to miners as the transaction fee. Nothing is wasted, nothing is created. Every satoshi is accounted for.

Inputs, Outputs, and Change Addresses

Now let’s talk about UTXOs — Unspent Transaction Outputs. The name sounds technical, but the concept is simple. A UTXO is a chunk of Bitcoin you’ve received that hasn’t been spent yet. Think of your Bitcoin wallet not as a bank account with one balance, but as a physical wallet full of different bills. You might have a $20, a $10, and two $5s. Your total is $40, but it exists as four separate pieces. UTXOs work the same way. Your Bitcoin balance is a collection of specific, separate outputs from previous transactions — each a distinct amount, linked to a specific address you control. When you send Bitcoin, your wallet selects one or more UTXOs as inputs, spends them in full, and creates new outputs for the recipient and for your change.

Why does this matter for security? A few reasons. First, your wallet has to manage UTXO selection carefully. If you have twenty small UTXOs and you want to send Bitcoin, your wallet may need to combine several of them — and that combination reveals to the blockchain that all those UTXOs likely belong to the same wallet. Think of it like paying for a large purchase with coins from twenty different pockets — the cashier now knows all those pockets belong to you. This is called the “common input ownership heuristic,” and it’s one of the primary techniques chain analysis companies use to map Bitcoin activity back to individuals.

Second, each UTXO is tied to a specific address. This is exactly why the address reuse rule we covered in Lesson 1.3 matters so much in practice: if you receive multiple UTXOs to the same address and then spend them together, you’ve made it trivially easy for anyone to see your total holdings and transaction history at that address. Different addresses for different UTXOs keeps them compartmentalised — like keeping different assets in separate safes rather than piling everything into one. We’ll go much deeper into UTXO management, coin control, and labelling in Module 5 when we cover chain analysis and privacy strategies.

Change addresses are something most beginners never think about. When your wallet spends a UTXO, it creates a new output for your change — and it sends that change to a brand-new address inside your own wallet. This is automatic and correct behavior in any reputable wallet. But here is the security implication: if you’re manually constructing transactions, or using a watch-only wallet, always verify your change address before broadcasting. An attacker who can modify your transaction can replace your change address with their own — and quietly steal everything that was supposed to come back to you. Always verify on your hardware device screen.

Transaction Fees and Mempool Dynamics

Before a transaction is confirmed, it lives in the mempool — the memory pool. This is a holding area, maintained by Bitcoin nodes worldwide, where unconfirmed transactions wait to be picked up by a miner and included in a block. The mempool is not one single thing — every node has its own view of pending transactions. But they largely agree on what’s waiting. And crucially, miners choose which transactions to include in each block based on the fee offered.

Fees are measured in satoshis per virtual byte — or ‘sats per vbyte.’ Think of it like postage: a heavier package costs more to ship. In Bitcoin, a more complex transaction (one that uses more data) costs more in fees. And just like express shipping costs more than standard, paying a higher fee rate gets your transaction processed faster. When network activity is low, even a 1 to 2 sat/vbyte fee may confirm in the next block. When activity spikes — during a bull run, a major on-chain event, or an ordinals inscription wave — fees can rise dramatically and underpaid transactions can wait hours or even days. The fee market is dynamic. Always check current conditions before you send, especially for time-sensitive transactions.

The good news: most modern wallets and hardware wallet companion apps will suggest fee rates based on current mempool conditions. For the most accurate real-time view, mempool.space is the go-to public tool. It’s free, open source, and shows you exactly how congested the network is and what fee rate you need to get confirmed in your target timeframe. Bookmark it. You’ll use it regularly as a Bitcoin holder.

Reading a Block Explorer: mempool.space Walkthrough

A block explorer is a public interface for reading the Bitcoin blockchain — think of it as a search engine for Bitcoin transactions. Every confirmed transaction, every block, every address — all publicly visible, permanently. Let’s walk through what you see on mempool.space. At the top is the Transaction ID — the TXID — a unique 64-character hash that identifies this specific transaction. Below that are two columns: inputs on the left and outputs on the right. Each input shows the address that was spent and the amount. Each output shows the destination address and the amount received.

Below the inputs and outputs you’ll see the fee paid and the fee rate in sats per vbyte. You’ll also see how many confirmations the transaction has — each confirmation means one additional block has been mined on top of the block that included your transaction. One confirmation means your transaction is in the blockchain. Six confirmations is the traditional standard for considering a large transaction fully settled — enough accumulated Proof of Work sits on top that reversing it would be economically catastrophic for any attacker.

Block explorers are powerful tools for your everyday Bitcoin life. Use one to verify that a transaction you’ve sent has been confirmed. Use one to show proof of payment. Use one to investigate an address you’re curious about. Use one to look up your own receiving addresses and confirm that a deposit arrived. Get comfortable reading them — mempool.space in particular. It’s one of the most important tools in your Bitcoin security toolkit.

The 21 Million Cap and Why It Matters

Twenty-one million. That is the total number of Bitcoin that will ever exist. Not 21 million today with more to come. Not 21 million unless the protocol is changed. Twenty-one million, full stop. This cap is written directly into Bitcoin’s code and enforced by every node on the network. No government, no company, no foundation, no group of miners can change it without the consensus of the entire network — which means in practice it cannot change at all.

Compare this to every fiat currency in existence. The US dollar has no hard cap. The Federal Reserve can create new dollars at any time — and does. Since 2020, the US money supply has expanded massively. Every new dollar created dilutes the purchasing power of the dollars you already hold. This is not a conspiracy theory — it is a mechanical consequence of unlimited money creation. Bitcoin was designed to be the opposite: a money where no one can inflate your holdings away.

Of the 21 million Bitcoin, approximately 19.8 million have already been mined. The remaining 1.2 million or so will be released slowly over the next century — with the last Bitcoin mined sometime around the year 2140. The issuance schedule is not random. It is governed by a mechanism called the block subsidy and an event called the halving. Understanding these two things explains everything about Bitcoin’s monetary policy.

The Block Subsidy and the Halving Schedule

When a miner successfully adds a new block to the blockchain — by solving the Proof of Work puzzle we covered in Lesson 1.2 — they receive two things. First, all the transaction fees from the transactions included in that block. Second, a freshly created amount of Bitcoin called the block subsidy. This subsidy is the only mechanism by which new Bitcoin enters existence. There is no central bank issuing Bitcoin. There is no company minting it. New Bitcoin comes into being only through this process, one block at a time, roughly every ten minutes.

Every 210,000 blocks — roughly every four years — this block subsidy is cut in half. This event is called the halving. When Bitcoin launched in 2009, the block subsidy was 50 Bitcoin per block. In 2012 it halved to 25. In 2016 to 12.5. In 2020 to 6.25. In April 2024, the most recent halving brought it to 3.125 Bitcoin per block. The next halving will bring it to 1.5625. This process of successive halvings continues until the subsidy reaches zero — at which point all 21 million Bitcoin will have been issued, and miners will operate solely on transaction fees.

What makes this issuance schedule remarkable is not just the cap — it’s the predictability. You can calculate exactly how many Bitcoin will exist on any future date. You can verify the total supply right now by running a full node. There is no opacity, no committee, no discretion. The monetary policy of Bitcoin is the most transparent and auditable in the history of money.

Bitcoin vs. Gold: Digital Scarcity

Bitcoin is often compared to gold, and the comparison is useful up to a point. Both are scarce. Both require work to produce. Both have historically been used as stores of value. But there is a critical difference: nobody knows exactly how much gold exists in the earth’s crust, and new gold is mined every year, slowly inflating the supply. Bitcoin’s supply is mathematically certain and completely transparent. Every Bitcoin that will ever exist is accounted for in the protocol.

Gold is also physically heavy, difficult to transport, impossible to verify without specialist equipment, and easily seized at borders. Bitcoin, by contrast, can be stored in your head as a 12-word seed phrase. It can be transmitted across the internet to anywhere in the world in minutes, for minimal cost, with no intermediary. This is what people mean when they say Bitcoin is digital gold — and in several important ways, it is an improvement on the original.

Economists use a concept called the stock-to-flow ratio to measure scarcity. In simple terms, it asks: how much of something already exists compared to how much new supply is being created each year? A high ratio means very little new supply is entering the market relative to what’s already out there — which is what makes something scarce and valuable. Gold has historically had one of the highest stock-to-flow ratios of any commodity, which is part of why it has been a reliable store of value. After the 2024 halving, Bitcoin’s stock-to-flow ratio surpassed gold’s. And it will double again with every future halving. This is a property no commodity in the physical world can replicate.