◄►▲▼ - Move
Z - Swing
X - Power Shot
Hitting the ball when it is directly in front of you will return in the direction it came from. Standing to the left or right of the ball when hitting it will angle your shot. The further to the side of the ball you are the more angle your shot will have.
Whenever you return the ball during a rally you will build up power. You can do a power shot anytime you have power in your meter. The more it builds up the faster your shot will be.