You can control Red from WASD key Arrow keys or if you're playing in smartphone you can thouch the control that at bottom of screen. And you can kill the flying enemy and walking enemy by jumping on them (Mario style). And if you have collected all three keys you'll be able to complete that particular level, if not, the door at the last of the level will remain locked and you'll be not able to complete that particular level. There are 4 level. Easy. Try it out!