What Is Ethereum? Smart Contracts, Explained Simply

Ethereum is a blockchain you can program, and smart contracts are the little programs that run on it. Where Bitcoin is designed mainly to move one cryptocurrency around, Ethereum adds a computer that everyone shares, so developers can build applications that hold and move value automatically according to rules written in code. Launched in 2015, it is the second-largest crypto network and the home of most tokens, stablecoins and NFTs. This guide explains smart contracts, the coin called ether, the fees called gas, and why all this power comes with its own risks — without the usual jargon.

What a smart contract really is

A smart contract is a program that lives on the blockchain and runs exactly as written, with no one able to stop it or change its mind. The classic analogy is a vending machine: you put in the right coins, press the button, and the machine releases your snack automatically — no shopkeeper needed, and no discretion. A smart contract is a digital version of that idea for money and data. It might say 'if this person sends 100 dollars of crypto, release the digital ticket to them,' and it will carry that out on its own, the same way every time. The appeal is automation without a trusted middleman; the danger is that 'runs exactly as written' includes running exactly the bugs and loopholes that were written, which attackers hunt for.

A smart contract does not know fairness or intent. It does what its code says, to the letter — which is a strength when the code is sound and a catastrophe when it is not. Billions have been lost to flawed contracts that did precisely what they were told.

Ether and gas: the fuel of the network

Ether, or ETH, is Ethereum's native coin, and it plays two roles: it is a cryptocurrency you can hold and send, and it is what you spend to use the network. Every action on Ethereum — sending ether, using a smart contract — costs a fee called gas, paid in ether, which compensates the computers that run the network and prevents people from clogging it with junk. Gas fees rise and fall with demand, so at busy times a simple transaction can become surprisingly expensive, and at quiet times it is cheap. Understanding gas is important before you ever interact with Ethereum, because an unexpected fee is a common and unpleasant beginner surprise.

From mining to staking: the Merge

For its first years, Ethereum was secured by mining, just like Bitcoin. In September 2022, in an upgrade known as the Merge, it switched to proof of stake, where validators lock up ether as a security deposit instead of burning electricity. The change cut Ethereum's energy use by more than 99% and is the reason staking is now such a common word in crypto. If the terms proof of work and proof of stake are unfamiliar, our guide to how a blockchain works explains both. The takeaway is that Ethereum today is secured by people staking coins rather than running power-hungry machines.

Why most tokens and NFTs live on Ethereum

Because Ethereum lets anyone deploy a smart contract, it became the default place to create new tokens. A token is just a smart contract that keeps track of balances, so launching one takes minutes and very little money. That openness is why Ethereum hosts thousands of tokens, most stablecoins, and the bulk of NFTs — and also why it hosts an enormous amount of junk and outright fraud, since the same ease that lets a legitimate project launch lets a scammer launch too. We draw the line between a network's own coin and the tokens built on top of it in coins versus tokens. The lesson for a beginner is that a token being 'on Ethereum' says nothing about whether it is trustworthy.

The risks that come with programmability

Ethereum's flexibility is also its risk surface. Smart contracts can contain bugs that drain them; 'decentralised finance' apps built on them can fail in complex ways; and approving a malicious contract in your wallet can let it empty your funds, a trick behind many thefts. None of this means Ethereum is a scam — it is genuinely important infrastructure — but it does mean the space around it is more dangerous for beginners than plain Bitcoin, because there are far more ways to lose money. Learn how the pieces work before you touch any of them, keep amounts small, and treat every unfamiliar app and token as guilty until proven innocent. As always, nothing here is financial advice.

What people build on Ethereum

Smart contracts make Ethereum a platform, so a whole ecosystem has grown on top of it. The biggest category is decentralised finance, or DeFi: apps that let people lend, borrow, trade and earn interest through smart contracts instead of banks. Alongside it sit marketplaces for NFTs, blockchain-based games, and tools for creating and managing tokens and online communities. Much of this is genuinely experimental and some of it is useful, but it is also where a lot of risk concentrates: DeFi apps can be complex, interdependent and buggy, and losses cascade when one fails. For a beginner, the important thing is not to master every app but to recognise that 'built on Ethereum' spans everything from serious infrastructure to outright casinos, and the label alone does not tell you which is which.

Layer 2s and fees, briefly

One practical thing you will hear about is 'layer 2s.' Because Ethereum's popularity can make gas fees high, developers built additional networks that sit on top of Ethereum, bundling many transactions together and settling them back to the main chain more cheaply. These layer-2 networks let people transact for a fraction of the cost while still relying on Ethereum's security. You do not need to understand their inner workings to use crypto, but it helps to know why someone might tell you to move funds to a layer 2 to save on fees, and that doing so adds another step — and another place where a mistake or a fake site can catch you out. As always, go slowly, and treat any unfamiliar network or bridge with caution.