As you explore crypto you will meet two kinds of exchange, and understanding how they differ helps you know what you are trusting in each case.
A centralized exchange is run by a company. You create an account, often deposit funds into it, and the company matches buyers and sellers and holds crypto on your behalf. This is usually the easiest on-ramp for beginners, with familiar logins and support, but it means trusting the company with your funds and your data.
A decentralized exchange, often shortened to DEX, works differently. There is no company holding your money. You connect your own wallet and trade directly with smart contracts that handle the swap automatically. You keep control of your keys the whole time, but you also take on more responsibility, since there is no support desk and mistakes are your own.
In short: a centralized exchange trades convenience for trust in a company, while a decentralized one trades self-reliance for keeping control of your own funds throughout.
