As you hit each ball out you gain experience points (xp). The harder you hit the ball, the more xp you collect. At the end of each level you can spend this xp on one or more of four upgrades - size, speed, white ball size and boundary area. You'll need to upgrade to face faster, bigger balls and make it all the way past level 50 to pass the game.
Swing ('zwing') your ball around using the mouse, smashing all the black balls of screen. Your aim is to protect the white ball in the centre. If the white ball leaves the boundary, it's game 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.