Basically, the game consists of a board of randomly placed coloured balls. You can select a ball and swap it with any adjacent ball which is to the left, right, above or below it. Diagonal moves are not allowed.
If the resulting swap results in a horizontal or vertical row of three or more balls of the same colour, those balls are removed from the board and replaced by random coloured balls.
Points are awarded for each set of removed balls, with bonuses for forming rows of 4 or 5 balls. When the balls are replaced, they may form other rows and columns which are also removed - called 'cascades' - with further points awarded. The object is to score as many points before there are no more goes left.
There are alternative playing pieces, as well as hint and preview modes.
Although the game is 2D, there is also a 3D version hidden away inside it which is only playable after you have reached a certain score on the hiscore table. Even when this score has been reached, you still have to figure out how to access it!