Web3 Blockchain Basics
Blockchain is the technology that powers Web3. Everything in Web3 — from cryptocurrency to digital ownership — runs on a blockchain. Once you understand how it works, the rest of Web3 becomes much easier to grasp.
What Is a Blockchain?
A blockchain is a shared record book that thousands of computers maintain at the same time. Every time someone makes a transaction, it gets recorded in this book. No single person or company controls it.
The Ledger Analogy
Imagine a village where everyone keeps the same notebook. Every time someone buys or sells something, every villager writes it down in their own notebook. To change a past record, you would have to change everyone's notebook at the same time — which is nearly impossible.
That is how a blockchain works. The "notebook" is shared across thousands of computers.
How a Blockchain Is Built
Data on a blockchain is stored in blocks. Each block holds a batch of transactions. Blocks link to each other in order — forming a chain.
[Block 1]──►[Block 2]──►[Block 3]──►[Block 4] Genesis Jan 5th Jan 6th Jan 7th Block Txns Txns Txns ↑ Cannot be changed without breaking every block after it
What Each Block Contains
- Transaction data — who sent what to whom
- Timestamp — exactly when it happened
- Hash — a unique fingerprint of this block's data
- Previous hash — the fingerprint of the block before it
If someone tampers with Block 2, its fingerprint changes. That breaks Block 3's link. Then Block 4 breaks. The whole chain rejects the tampered version automatically.
Who Keeps the Blockchain Running?
Thousands of computers called nodes store a full copy of the blockchain. They constantly check each other's copies to make sure everyone agrees on what the record says.
This agreement process is called consensus. No single node can cheat, because the majority will always outvote it.
Key Properties of a Blockchain
| Property | What It Means | Why It Matters |
|---|---|---|
| Decentralized | No single owner | No one can shut it down |
| Immutable | Past records cannot change | Transactions are permanent |
| Transparent | Anyone can view records | Easy to verify and audit |
| Trustless | No middleman needed | Code enforces the rules |
Public vs. Private Blockchains
Public Blockchain
Anyone can join, read, and write. Bitcoin and Ethereum are public blockchains. No permission needed to use them.
Private Blockchain
Access is restricted to invited participants. Companies use these for internal record-keeping. They are faster but less decentralized.
A Real-World Example: Sending Crypto
You send 1 ETH to a friend. Here is what happens step by step:
- Your transaction broadcasts to thousands of nodes
- Nodes verify you actually have 1 ETH and the transaction is valid
- The transaction groups with others into a new block
- The block gets added to the chain permanently
- Your friend's wallet shows the balance update
The whole process takes seconds to minutes, depending on the network. No bank. No waiting days. No approval required.
Common Blockchains in Web3
- Bitcoin — the original blockchain; mainly used for storing and transferring value
- Ethereum — the most widely used for Web3 apps and smart contracts
- Solana — fast and low-cost; popular for gaming and NFT projects
- Polygon — a cheaper, faster layer built on top of Ethereum
What Blockchain Is Not
- Blockchain is not the same as cryptocurrency — crypto runs on a blockchain
- Blockchain is not 100% anonymous — most are transparent and traceable
- Blockchain is not just for finance — it powers identity, gaming, art, and more