Shooting in the game is accomplished by pressing and holding the shoot button. Release it at the apex of your character's jump to give you the best chance at scoring.
Many times, it's best to let the AI on your team handle the defense. The questionable responsiveness of the controls often leads to more fouls than steals if you try to strip the ball.
Try to put a little space between your shooting character and the nearest defender before attempting a basket. Much as in real basketball, this allows for greater accuracy in your shots.