How Bitcoin Actually Works, Step by Step

The best way to understand Bitcoin is to follow one payment through the system and watch what each part of the machinery does to it.

What you actually own

There are no bitcoins in a wallet. There is no file containing coins. What exists is a public ledger recording that certain amounts are spendable by whoever can produce a valid signature for a given address.

Your wallet holds a private key — a very large random number. From it, one-way mathematics derives a public key, and from that, an address. The relationship runs in one direction only: an address reveals nothing useful about the private key that controls it.

The private key's only job is to produce digital signatures. When you spend, your wallet signs the transaction, and anyone can verify that the signature matches the address without ever seeing the key. This is why “not your keys, not your coins” is not a slogan but a literal description: whoever holds the key holds the authority, and there is nothing else to hold.

Unspent outputs, not balances

Bitcoin does not store account balances. It stores unspent transaction outputs, or UTXOs — discrete chunks of value, each locked to an address. Your wallet's displayed balance is simply the sum of the chunks it can unlock.

This has a consequence that confuses newcomers. UTXOs are spent whole, like cash. If you hold a single 0.5 BTC output and want to send 0.2 BTC, the transaction consumes the entire 0.5 and creates two new outputs: 0.2 to the recipient and roughly 0.3 back to a change address you control.

The fee is never stated explicitly. It is whatever the inputs exceed the outputs by, and miners collect it. This is also why transaction size is measured in bytes rather than value: a transaction consuming many small UTXOs is physically larger and costs more to send than one consuming a single large one, regardless of the amount being moved.

The journey of a transaction

1. Construction. Your wallet selects inputs, builds the outputs, and signs with your private key.
2. Broadcast. The signed transaction goes to a few connected nodes, which relay it to their peers. Within seconds it has propagated across the network.
3. Validation. Every node independently checks it: is the signature valid, do the inputs exist and remain unspent, do the numbers balance? Invalid transactions are dropped, not forwarded.
4. The mempool. Valid but unconfirmed transactions wait in each node's memory pool. Miners choose from here, and they choose by fee rate — satoshis per byte — because block space is limited.
5. Mining. A miner assembles a candidate block and searches for a nonce that makes the block's hash fall below the difficulty target. This takes roughly ten minutes across the whole network, by design.
6. Propagation and confirmation. The successful block is broadcast, other nodes verify it, and your transaction now has one confirmation. Each subsequent block adds another.

Confirmations, difficulty and the halving

Confirmations are a probabilistic measure of finality. Reversing a transaction means producing a longer competing chain from before it, which gets exponentially harder with each block added. One confirmation is usually fine for small amounts; six — about an hour — is the traditional threshold for large ones.

Difficulty adjustment keeps the ten-minute target stable. Every 2,016 blocks, roughly two weeks, the network recalculates how hard the hashing puzzle must be based on how fast the previous blocks arrived. More miners means higher difficulty; miners leaving means it falls. This self-correction is what keeps issuance predictable regardless of how much computing power joins.

The halving enforces the supply cap. Miners receive newly created bitcoin as a block subsidy, and that subsidy halves every 210,000 blocks — about four years. It began at 50 BTC, and the geometric series converges to just under 21 million coins, with the last fraction issued around 2140. After that, miners are paid by transaction fees alone.