What is blockchain?
A public ledger nobody can edit.

Blockchain, explained with a ledger

Imagine a village with no bank. Everyone agrees that each person keeps an identical ledger. When someone pays someone else, they announce it and everyone writes it down.

1. Every so often, recent payments are bundled into a page. That page is a block.
2. Each page carries a “fingerprint” (hash) of the page before it, so pages link into a chain.
3. Secretly changing an earlier page breaks every fingerprint after it, and everyone notices.
4. Who writes the next page? Bitcoin runs a computing race (mining); Ethereum picks from people who lock up coins (staking).

What does decentralized mean?

Centralized means one party is in charge, like a bank that alone can edit its books. Decentralized means no single party is in charge: many participants keep the ledger, so one of them going offline or cheating doesn’t matter.

Note that exchanges are centralized. Coins in your OKX account are held by the platform, so a forgotten password can be recovered. Moving them to your own wallet is what real self-custody means.

What is a public blockchain? Which ones matter?

A public chain is one anyone can join, read and use. Each has a native coin used to pay fees.

The key lesson: the same coin on different chains uses different networks, and choosing the wrong one when withdrawing can lose funds.

What is a smart contract?

A smart contract is a program stored on a blockchain that runs automatically when its conditions are met, with nobody able to change it midway. For example: “when 1 ETH arrives, send back 3,000 tokens”, no middleman needed.

• Decentralized exchanges, lending, stablecoins and NFTs are all smart contracts underneath.
• Buggy code can be exploited; many contracts have been drained by hackers.
• The most common beginner risk is “approvals”: approving a contract on a shady site can let it move coins out of your wallet.

Why do I pay gas fees?

Every action on a public chain pays a small fee to whoever records it; on Ethereum it’s called gas. The busier the network, the higher the fee.

How do wallet addresses, public keys and private keys relate?

Think of it this way: a wallet address is like an account number you can share so people can pay you; a private key is like your PIN plus signature, and whoever has it can move the coins. The public key is derived from the private key and the address from the public key, and none of it can be reversed.

What is Layer 2? A layer 2 is a “fast lane” built on top of a main chain like Ethereum. It bundles many transactions and settles them back on the main chain, so it’s faster and cheaper. OKX’s X Layer, Arbitrum and Base are examples.