Its a numbers puzzle. The aim of the game is to get each number on a 3x3 board of numbers to be exactly the same. One of the numbers is always selected. Each time you move the selector, the number you select next will increase by one.
Starting from the level 51 it becomes a little more complicated. The board contains dark and bright tiles, each of which has different behavior. Stepping on bright tiles increases the numbers by one, whereas stepping on dark tiles decreases the numbers by one.