Help with a 3D GameObject GUI

I’m looking for a tutorial/help on how to make a properly functioning Title Screen.

What I want to end up with is using an xbox 360 remote as the controller, and being able to use game objects for my GUI, for example tying in an OnMouseDown command to a game object,

But I have no idea how to attach one such command to a game object, and what the command is for let’s say the “A” on the remote.

Help?

My guess would be that “A” is one of the Input axis.