You have seen why someone might want open money that no single organization runs. Now we need to make it work. Imagine paying a friend over the internet, with no bank in the middle deciding whose balance changes.
There are two questions to answer. First, is the sender allowed to spend this money? This is called authorization. Second, has the same money already been spent somewhere else? Keep these two questions separate as you read.
First, solve the copying problem
A photo is easy to send because it is easy to copy. You keep yours, and your friend gets another. Try that with money and the same value could be spent over and over.
When you hand over a paper banknote, it leaves your hand. You cannot spend it twice. A digital payment needs another way to prove the same money was not already spent. This is called the double-spending problem. It is the first problem to solve for money without a central bookkeeper.
Someone has to keep the record
In a normal payment system, a bank or company keeps track of balances. It decides whether each payment can go through. Bitcoin takes on a different challenge. It lets many computers on a network check one shared history of transactions, with no single bookkeeper in charge.
Drawing a digital coin is easy. The hard part is this: how do strangers agree on a payment history when someone might be trying to cheat?
One name, two meanings
Bitcoin with a capital B is the name of the network and its rules. A bitcoin with a small b is one unit of the money used on that network. It is often written BTC. So the network processes transactions, and BTC is what those transactions move.
Bitcoin was first described in a 2008 white paper, a short document explaining an idea. It was published under the name Satoshi Nakamoto. The network began operating in 2009. You do not need to solve the mystery of who Satoshi is to check the system. The rules are written in software that anyone can read and run.
Three pieces make the idea work
Your wallet uses secret keys to authorize spending. A full node is a computer that checks whether transactions and blocks follow the rules it enforces. A block is a batch of transactions added to the shared history. Miners compete to add the next block.
Those jobs fit together, but they are different jobs. One cannot replace another. Owning a powerful miner does not give you somebody else’s keys. Running a node does not create a reward for you. And a wallet is not a little hard drive full of coin-shaped files.
A history that gets expensive to replace
Imagine two competing versions of the same payment history. Nodes follow the valid chain of blocks with the most total proof of work. Proof of work is the huge amount of computing effort miners spend to produce each block. To replace a payment already in a block, an attacker must redo the work for that block and every block after it. Then their chain must have more total work than the chain everyone else keeps building.
The block that includes your payment, and each block added after it, counts as a confirmation. Each additional confirmation adds work an attacker would have to overcome. That makes reversal harder. It does not make every payment final the instant it is sent, or impossible to reverse in theory. This is where the machines on the mining floor enter the story.
The floor is connected to something much bigger
A hashboard is the board of chips inside a miner that does the mining work. When you bring a hashboard back online, it rejoins this competition. Its work helps extend a history that anyone can check for themselves.
You also do not need a whole bitcoin to use the system. One bitcoin divides into 100 million smaller units called satoshis, or sats. The interesting question is how that value can move between people who have never met.
You can start to understand this without buying a miner or becoming an expert in the math behind it. Ask a question. Follow a transaction. Learn what a node actually checks. Each step helps you judge the system for yourself.
What does this change for the person paying?
You can use a wallet to authorize a payment yourself. You do not have to ask a bank to update its private ledger. That is the big change worth understanding. It does not mean every payment is instant, free or anonymous. Each block has limited space, so transactions compete to get in, and confirmation takes time.
It also does not make the bitcoin price stable. The network’s rules and the price people will pay for BTC are different things. For now, focus on the question the technology answers: who can spend which funds, and how can everybody else check?
Optional reading for this lesson
Continue your study
Reading for this lesson
Start with the problem in the introduction.
Visual explanations of Bitcoin concepts.