Exchanges help users swap fiat currencies like USD or EUR for Bitcoin, or trade BTC against altcoins. Centralized exchanges (CEXs) are run by a company holding user funds and matching orders internally. Decentralized exchanges (DEXs) operate without a single custodian; users trade directly from their wallets, often facilitated by smart contracts or peer-to-peer matching.

Both formats differ in liquidity, user experience, and regulatory compliance. CEXs typically have higher volumes and simpler interfaces but require trusting the platform with your private keys. DEXs minimize trust but can feel more complex and sometimes have lower liquidity. Most Bitcoin newcomers start on a CEX for convenience, but many graduate to DEXs or self-custody once they grasp the importance of holding private keys.