As the GBA has a limited amount of buttons,
Ultimate Beach Soccer also carries a limited amount of controls for you to utilize in the game. Pass and shoot will be your two main weapons, and as you get better at that you can utilize the derivatives thereof, like one time shots and thru passes.
Unfortunately, controlling the actual players on the pitch is almost impossible. The computer sporadically changes your control of a player when you don't have the ball, and when you do, you often lose control of it for no apparent reason. Robot dogs playing this sport would look smoother than this game does in action.
For all its simplicity, Ultimate Beach Soccer ultimately fails. The only game option, which is to play a game, isn't all that good, and will leave you with a hollow feeling inside if you play for too long, the same kind of feeling you get when you watch too much spirit crushing TV. If you have any interest in the actual sport of Beach Soccer, I suggest you stay away from this game so as not to tarnish any image you may already have of it.