Touch o mobile device.
Mouse or keyboard(Arrow key) o PC.

There are two squares attached to each other at the center of the screen. They are in two different colors, blue and red and you can turn them by touching sides of the screen or clicking on arrows. Also there are squares entering from different sides of the screen with the same blue or red colors. You have to turn the center squares so that squares with the same colors match each other when they reach the center. If you fail to do so, you will lose.