How do I send a friend invite on Xbox 360?

Hi I play Viva Pinata on Xbox 360 all the time and I really want to trade pinatas with someone but I don't know how. Don't I have to like add them as a friend and stuff? How do I do that? Can someone explain to me the process?
How do I send a friend invite on Xbox 360?
well, if you have live and know their gamertag, type it in after you hit the "add friend" in the friends menu, after you hit the middle button...