Youre a small gray dot that must avoid the other dots. But when you turn green, thats your time to strike. Press and hold anywhere on the screen to grow spikes, then move into another dot to pop it. The ensuing explosion can pop other dots for a chain reaction.
More explosions in a single chain results in a higher score. But dont get too greedy. Retreat to the edges of the screen to end your combo early and shrink back to your original size.