You tilt your phone to move three balls through a ringed maze toward the center. It's a simple goal, but all the balls respond to the same tilt at once, so getting one where you want it tends to move the others somewhere you don't.
There are four game levels, all available from the start. The earlier ones give you room to figure out how the movement works, and the later ones introduce rings that rotate on their own, shifting the paths through the maze as you play. And more balls. A timer is optional if you want something to measure yourself against.