Back to: Smart Contracts for Beginners
Calling a contract means sending a transaction to its address with instructions (“swap X for Y,” “deposit Z”). Every node then re-runs your call to verify the result — thousands of computers repeating your computation so no one has to trust anyone.
Gas: paying for every step
Each operation costs gas: simple transfers are cheap, complex contract calls cost more. You set a max fee; validators take the highest bidders first. Failed transactions still consume gas — the network did the work even though your call reverted.
The EVM in one paragraph
Ethereum’s computer (the EVM) is deliberately simple and deterministic: same input + same chain state = same output, on every node, forever. Determinism is what makes decentralized verification possible — and why contracts can’t use randomness, clocks, or web data without help (oracles, commit-reveal schemes).
Success vs revert
– Success: state changes, events logged, gas consumed. – Revert: a require failed (bad input, insufficient balance, expired deadline) — state rolls back, but gas is still spent. Reverts protect you; they are not errors to fear.
Reading a transaction (try it)
Open any contract interaction on an explorer: From (you), To (contract), Value, Input Data (the encoded call), gas used, and Logs (what the contract announced). Those five fields are the complete story of every dApp action you’ll ever take.
Execution is public rehearsal: your call performs on every node
> simultaneously, and the audience verifies each line.
Next lesson: walkthrough of a real (simple) contract.