Get the combination right and switch off all the lights on the grid as fast as possible.
Using the mouse click lights. Clicking a light will switch the lights next to the one you just pressed either on or off. If they were on they will switch off, and vice versa. By clicking the correct sequence try to turn all of the lights to the off position. Hint: You will never have to press the same light more than once!
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.