"Zwing" your ball around using the mouse, smashing all the black balls of screen. The aim is to protect the white ball in the centre at all times. If the white ball leaves the boundary, the game's over. Every 10 levels, you'll face a boss that you have to continually hit until he runs out of health and goes off screen.
As you hit each ball out of the screen, you gain experience points (xp). The harder you hit the ball, the more xp you collect.