How to use the Game chat on Xbox 360?

So, me and my friend were playing minecraft, we were both curious on what it was, so we went on the party options and clicked on game chat, but it just muted us, so we're trying to get it to work, can someone tell us how it works please? It might just be for games like COD or something, but I want to know how it works, reply As Soon As Possible please!