Exchanges come in two forms: centralized and decentralized. A centralized exchange manages the trading of assets like cryptocurrencies, forex, and commodities. The exchange acts as an intermediary between market participants and as a custodian of the traded assets. To use a centralized exchange, you have to load up your account with the fiat or crypto you want to trade.
A serious centralized exchange needs to make sure transactions occur smoothly. Other responsibilities include regulatory compliance, KYC (Know Your Customer), fair pricing, security, and customer protection. In return, the exchange charges fees on transactions, listings, and other trading activities. Because of this, exchanges can profit in both bull and bear markets, as long as they have enough users and trading volume.