Two squares enter the screen and move toward each other. All you have to do is touch either side of the screen to jump over the other square. But note that only the big one can successfully jump over the small one. So you have to be quick to decide which side of the screen to tap and time your jumping in order to avoid hitting the other square. Note that it is not an easy game and it even becomes more difficult as you progress because these squares will move faster and faster!
Touch on mobile device or mouse on PC.