Almost everyone's first step into crypto is an exchange, yet most people use one without really knowing what happens under the hood. Understanding how exchanges work demystifies where prices come from, why fees exist, and — most importantly — where your money is actually sitting when you leave it on a platform. That last point has cost people fortunes, so it is worth getting right.
What an exchange is for
At its simplest, a crypto exchange is a marketplace that connects people who want to buy crypto with people who want to sell it. It plays matchmaker, and in doing so it performs the price discovery that produces the numbers you see quoted across the crypto market.
But not all exchanges work the same way. The single biggest divide is between centralized and decentralized exchanges, and the difference has everything to do with who holds your money.
Centralized exchanges (CEXs)
A centralized exchange is a company that runs the marketplace — the kind of platform most beginners start with. It feels a lot like an online brokerage or bank. You create an account, verify your identity, deposit funds, and trade through their app or website.
Behind the scenes, the heart of a centralized exchange is the order book: a live, constantly updating list of all the buy orders (bids) and sell orders (asks) for each asset.
- The bids are what buyers are willing to pay.
- The asks are what sellers want to receive.
- The gap between the highest bid and the lowest ask is the spread.
When you place a market order, the exchange matches you against the best available order on the opposite side, instantly. When you place a limit order, it sits in the order book until someone is willing to trade at your price. The "price" of an asset at any instant is simply where the most recent trades are matching. This is why prices can differ slightly between exchanges — each has its own separate order book.
Exchanges make money mainly through trading fees (a small percentage of each trade) and sometimes spreads and withdrawal fees. Understanding those costs is part of trading well, as covered in how to buy your first crypto safely.
The custody catch: not your keys, not your coins
Here is the crucial part beginners miss. When you hold crypto on a centralized exchange, the exchange controls the private keys, not you. Your balance is really a promise — an IOU in the company's database — rather than coins directly under your control.
Most of the time this is invisible and convenient. But it carries a real risk: if the exchange is hacked, becomes insolvent, freezes withdrawals, or turns out to be fraudulent, your funds can be lost or locked, even though the number in your account looked perfectly normal. History has several painful examples of large exchanges collapsing and taking customer funds with them.
This is the reasoning behind the crypto mantra "not your keys, not your coins." For active trading and small amounts, keeping funds on a reputable exchange is a reasonable convenience. For larger, longer-term holdings, moving crypto to a wallet you control reduces your dependence on any single company. If that distinction is fuzzy, read what is a crypto wallet, which explains custodial versus non-custodial storage in depth.
Decentralized exchanges (DEXs)
A decentralized exchange takes a very different approach: it removes the company from the middle entirely. Instead of a firm holding your funds and running an order book, a DEX uses smart contracts — self-executing code on a blockchain — to let people trade directly from their own wallets.
Many DEXs do not even use a traditional order book. Instead they rely on liquidity pools: communal pots of two assets that users deposit, with an algorithm setting the price based on the ratio between them. You trade against the pool rather than against a specific other person.
The appeal of a DEX is self-custody and openness — you keep control of your keys throughout, and anyone can use it without signing up. The trade-offs are real too: DEXs can be harder to use, you pay network fees for every action, prices can suffer slippage in thin pools, and a bug in the underlying smart contract can be exploited. They also run on the Layer 2 and base networks whose fees and speed shape the experience.
CEX vs DEX: which and when
Neither type is universally better; they suit different needs.
- Centralized exchanges are usually easier for beginners, offer customer support, handle the on-ramp from regular money, and provide deep liquidity. The cost is trusting a third party with custody.
- Decentralized exchanges offer self-custody and permissionless access, which appeals to more advanced users and those trading tokens not listed on big platforms. The cost is complexity and smart-contract risk.
Many people use both: a trusted centralized exchange as their on-ramp and for large trades, and a DEX when they want to stay in self-custody or access newer assets.
Using exchanges safely
However you trade, a few habits protect you:
- Choose reputable, regulated platforms and be deeply suspicious of any you first heard about through a DM or ad — a core lesson from spotting crypto scams.
- Secure your account with a strong password and app-based two-factor authentication.
- Do not treat an exchange as a long-term vault. Keep meaningful holdings in a wallet you control.
- Understand the fees before you trade, not after.
Once you can picture the order book matching buyers and sellers, the spread as the exchange's marketplace, and custody as the question of who really holds your coins, the whole machinery of crypto trading stops being a black box. Explore live prices and markets in our crypto section with that clearer picture in mind.