How do you make a sprite fall?

[TIMAI2]

Make a ball or sprite fall from random locations at the top of the screen

We are trying to make a ball (or sprite) fall from random locations across the top of the screen. The player will then move a basketball hoop left to right along the bottom to catch the ball. Once the ball is caught, another should drop from a random location on the top of the screen. We are having trouble getting the ball to actually drop, then get it to drop from random locations after it hits the hoop.