The controls for the 3-Point Contest are simple, but it'll take some practice to perform them in rapid succession. Your Mii will run to each basketball rack as you empty the previous one, but your position on the court has no effect on the controls.
First, tilt the Wii Remote down and press B to pick up a ball. You don't need to hold B like you do in bowling. Now, raise the controller up in the air to make your Mii jump and flick it upwards to shoot the ball. Keep your Wii Remote straight as you shoot. The amount of force required is something you'll learn with practice.
You don't have a lot of time here. If you want to get all of the balls in the hoop before the clock runs out, you'll need to pick up another ball and shoot it as you soon as you let go of the previous one.
In the Pickup Game mode, you'll play some 3-on-3. As with real basketball, you'll need to dribble the ball while you move. To do this, simply flick the Wii Remote down repeatedly, as if you were really dribbling. You can't control your Mii, but as long as you dribble, he or she will try to move towards the hoop.
You can pass to your teammates by hitting the button that's displayed over their head. This is the easiest way to get in close for a shot, but make sure you have a clear line to your teammate.
Shooting works the same as it does in the 3-Point Contest, but now you have somehow attempting to block you. When you jump up to shoot, don't take the shot if your opponent is in your face. Instead, wait for an opportunity where they jump too early or too late and leave you open for a shot.
If you're under the hoop, you can go for a slam dunk. When you're in position, hit B to jump into the air and then make a dunking motion with the Wii Remote for a guaranteed point.
You'll also get to play defense, which consists of stealing the ball and block shots. To steal the ball from whichever opponent you're guarding, just swing the Wii Remote. Make sure the ball is close enough to steal before you try this, because a failed attempt to steal will cause you to fall over and give your opponent an opening.
If the player you're guarding goes for a shot, flick the Wii Remote up just as they're about to shoot to leap up and block their shot. As long as you time it right, you'll deflect it. I'm blocked a lot of shots with my Mii's face, but they got blocked all the same.