What is a blockchain?
In one line: A blockchain is a shared record of transactions, kept by many computers at once, where new entries are added in linked blocks that are very hard to change later.
A simple picture
Think of a notebook that thousands of people hold a copy of. Every few minutes, a new page is added. Each page lists recent transactions, like "Address A sent 0.5 coins to Address B."
Each new page also carries a short code made from the page before it. That code is called a hash. Change one word on an old page and its code changes, which breaks every page after it. Everyone else's copy would show the mismatch.
That's a blockchain: pages are blocks, and the codes chain them together.
A simple example with numbers
On the Bitcoin network, a new block is added about every 10 minutes. That's roughly 144 blocks a day.
To rewrite a transaction from 6 blocks ago, someone would have to redo those 6 blocks and outpace the whole network while it keeps adding new ones. On a large network, that's extremely costly. That's why many people wait for several "confirmations" before treating a payment as final.
How the network agrees
Computers need a rule for who adds the next block. The two main ones are:
- Proof of work: computers race to solve a hard math puzzle. Bitcoin uses this.
- Proof of stake: holders lock up coins to earn the right to add blocks. Ethereum uses this.
Why it matters
It explains why crypto can move without a bank in the middle. It also explains why a sent transaction usually can't be reversed. There's no support line that can undo it.
See crypto trading for beginners for how this ties into trading.
A common mistake
Thinking "blockchain" means "safe investment." A blockchain can be secure while the coin on it falls 90%. Projects that use one can still fail, get hacked at the app level, or turn out to be scams.
Most of the public record can be viewed by anyone, with a "block explorer" website. Transactions show addresses, not names, but they aren't private.
Questions
Who controls a blockchain?
On public blockchains like Bitcoin and Ethereum, no single company. Many independent computers run the software and follow the same rules.
Can a blockchain be hacked?
Large public blockchains have proven very hard to rewrite. Most crypto losses come from hacked exchanges, apps, or stolen keys, not the chain itself.
Is blockchain only used for crypto?
Crypto is the best-known use. Others have been tried, like tracking supply chains, with mixed results.
Want the next step? We'll walk you through it.
Four free lessons by email, one every few days — each with a 10-minute exercise on a real chart.
Send Me the Free Lessons 4 short emails · No spam · Unsubscribe anytimeOr see the whole method, step by step:
See What’s Inside the Course Try everything free first. Decide when you're ready. · Open the free chart tool (works in the TradingView phone app)One chart idea a day, in plain English. Follow along: