It can be used in various ways:
* As a question word:
* "Quoi? Tu as dit quoi?" (What? What did you say?)
* "Quoi de neuf?" (What's new?)
* As an exclamation of surprise or disbelief:
* "Quoi! C'est incroyable!" (What! It's incredible!)
* "Quoi, tu es sérieux?" (What, are you serious?)
* As a synonym for "something" or "anything":
* "Il n'y a quoi que ce soit." (There's nothing.)
* "As-tu quoi que ce soit à dire?" (Do you have anything to say?)
It's important to understand the context to fully understand its meaning.