What a transaction is
A transaction is an instruction to the network signed with your key: "move X coins from address A to address B". The signature proves the owner of the address sent it — it cannot be forged without the private key.
A transaction's life cycle:
- The wallet builds the transaction and signs it.
- It lands in the mempool — the queue of pending transactions.
- A validator includes it in a block.
- The network confirms the block — the transaction becomes irreversible.
Irreversible — literally. Send to the wrong address and the funds are gone forever. There is no "cancel" button on a blockchain. Always check the first and last characters of the address before sending.
Gas — the network fee
Every transaction takes up block space and validators' compute. You pay for both with a fee — gas. How it works:
- A simple transfer is cheap — it's a primitive operation.
- Interacting with a smart contract (a swap, an NFT mint) costs more — more computation.
- Network congestion multiplies the price: when everyone rushes in at once, block space goes to auction.
Gas is paid in the network's native coin: ETH on Ethereum, BNB on BSC, SOL on Solana. Hence the rule: always keep a reserve of the native coin in your wallet, or you won't be able to move even your own tokens.
Typical costs
| Network | Simple transfer | DEX swap |
|---|---|---|
| Ethereum | $0.5–5 | $2–30 |
| Arbitrum, Base (L2) | $0.01–0.1 | $0.05–0.5 |
| BSC | $0.03–0.1 | $0.1–0.3 |
| Solana | ~$0.0003 | $0.001–0.01 |
The numbers float with coin prices and network load, but the ratio holds: L2s and Solana are hundreds of times cheaper than Ethereum.
Key takeaways
- A transaction is an instruction signed by a private key; once confirmed it is irreversible.
- Gas pays validators for block space; the price depends on operation complexity and network load.
- Gas is paid in the network's native coin — keep a reserve at all times.