All you have to do is find the right color. In order to kill the enemies waiting for you on the way, you must shoot them with bullets of their own color.
Change your bullet color by sliding the slider and start killing the enemies. You may encounter enemies of different sizes throughout your adventure. The number of bullets you need to hit will change according to their size. You can see the remaining health of your enemies from their healthbars. Try to kill them before they touch you because they will hurt you when they touch you. You can die when all your life is depleted, you have to be careful. You should be more careful especially against the enemies who are wearing helmets, remember that you have to shoot their helmets first.
Dead enemies will give you both money and paint. With the money earned, you can improve your weapon and make it shoot faster. You can also increase your total health.