Numbers will fall from the top. You can move them left or right as they fall using the arrow keys. You can tap the down arrow to drop a number quickly.
The numbers at the bottom represent a sum. You must pile numbers on top of those that add up to this sum. For instance, if the number at the bottom is 7, you can place a 2, 3, 1 and 1 on top of it do get 7. When you match the sum, you score that amount of points and the column is reset with a new number.
If you pass the sum by placing too many numbers of top of it, then column is stuck and can never be cleared.
If all columns are stuck, or you pile up too many numbers in a single column, the game ends.