Turn-Based matches

I’m looking at adding turn-based matchmaking with gamecenter to my game and have a few questions if anyone has any experience with it. I think I just need help with the initial setup. I can get the Multiplayer Game screen to come up to find a match but I don’t know what stores the data that transfers back and forth from the gamecenter and to the other player.

–What holds and transfers the match data? Is this the Turn Based Match Interface? If so how do you store the value in it?
–What is the Register Turn Based Interface Object used for?