Try putting tiles together to match numbers on tiles sides, it is that easy!
Well, in fact not that easy sometimes :)
Just pick a tile on the bottom or right board, and drag it to empty slot on the top or left.

If default 3 by 3 board seems too simple for you, then you could always try a 4 by 4 or 5 by 5 boards!

A colored theme is used by default, but if it looks too contrast for you - you could always switch to grayscale theme.

Can be played in portrait and landscape modes.