Who are these guys? And how do you make them do what you want them to do? Two very important fundamental questions I will try to answer!
THE A BUTTON A is the most fundamental button. It is pressed to lay a bomb. Also, if you have the throw prize, pushing it while on top of a bomb you dropped will heave it above your head. Letting go will send it flying in the direction you are facing. Pressing A while you have the throw and are on top of another player will lift them over your head!
THE B BUTTON B is used to try and get off another player when they are carrying you on their shoulders. Also, holding B and then moving in a direction will execute each character's special move.
THE X BUTTON X will stop all bombs of yours that are currently in motion because you or someone else has kicked them.
THE Y BUTTON Y starts out doing nothing. As you pick up more prizes, it becomes more and more useful. When you get the push prize, Y will make you shoot forward, attempting to push any players not on pets in your way. When you get the punch, pushing Y will allow you to punch any bomb in your path, booting it over a couple of blocks. When you get on a pet, Y will no longer be used for this purpose. It is then used to do the special move, if any, of the pet you are riding.