Click the mouse button once to choose the elevation, and then again for the amount of power. Getting the most from it is a little tricky. When you have sent the Berzerk ball going, you can guide it using the arrow keys to hit some of the bonuses or one of the rebound things.

Don't worry about the blood spurts when he hits the ground, this is a highly trained nerd. Besides, he has a wide range of snarky comments to say at you at the end.