To play, you click to shoot. Shooting the red dots will give you 1 point, but shoot the green one and you will lose a point. If you run into a red dot, you'll lose one health, but the green one will give you one if you touch it. Lose all your health and you will die and lose, but if you get a score of 100, you win! Watch out for your ammo! You can't get shoot anything if you run out of ammo. Click the reload button to regain ammo.
All credit goes to @ML39 I recommend checking out @huipowawae and @korenemy