Hit the shoot button while you don't have the ball, your dood will go for the alley-oop, then you just call for a pass. If you want the computer to go for the alley-oop, well... you really never know when he is going to go for it.
Why did the little girl drop her red ball? ...because she was getting kicked in the face.
An alley-oop is when a teammate jumps in the air and you throw it to them while they are in the air and they dunk.
The High-Flyer achievement means that you must catch and complete 10 alley-oops I believe.
You can alley-oop with the face buttons. Just press hold down turbo and press X while running to the basket, and while in the air, press B and you're teammate should pass it to you and you should dunk it(unless you get blocked of course).