This is a game of math and strategy. The game board consists of a grid of (blue) numbers and a bunch of (yellow) numbers. The object of the game is to use the yellow numbers to eliminate the blue numbers from the board.
To play, drag a yellow piece onto the boundary between two of the blue numbers. If the numerical difference between the two blue numbers is equal to the value displayed on the yellow number, the numbers will vanish and the board will readjust (empty columns/rows will collapse).