O que é o bitcoin exchange?

Could you please elaborate on what a bitcoin exchange is? I'm curious to understand its role in the cryptocurrency ecosystem. Specifically, how does it facilitate the buying and selling of Bitcoins? Is it a platform where individuals and institutions can trade Bitcoins securely? Additionally, what are some of the key features and considerations one should look for when choosing a Bitcoin exchange? I'm interested in understanding the process, security measures, and any potential risks involved in using such an exchange.