The object of the game is simple. Each level has a certain number of balls with a plus sign and a certain number with a minus sign. The idea is to get them to make contact, such that the positive and negative balls cancel each other out. But a given level may not have the same number of positive and negative balls, as you'll observe. That's okay, because if two different size balls collide, the smaller one will go away and the bigger one will get smaller. Have no fear – everything balances out in the end.