Aim for an imaginary dime on the lip of the rim. Most of your first couple of shots will probably clang off the rim or the backboard loudly. Not a problem! Shooting a ball into a hoop that high isn't easy, and it takes a lot of practice. It can be difficult to know exactly where to aim: the red square on the backboard? The top of the hoop? It can be helpful for some beginners to visualize a small coin balancing on the front lip of the rim, and that what you're trying to do is knock it off with your shot.
Most beginners aim too high, and this exercise trains the eye to lower the "sight picture" of the shot, aiming more at the rim. If your shots tend to be too low, change the exercise so that you're aiming at the back of the rim, where it connects to the backboard. This will do more to correct your aim.