There are a total of seven different worlds ranging from down under the sea, to being in space with asteroids. To help save the Earth you must go through each level and defeat the enemies. When you get to the end of each level you have to try and defeat the evil alien that is helping Emperor Bog. In order to get to the boss you have to find the colored keys that unlock the force fields. Then work your way towards the teleporter. You will receive passwords at the end of each level so you can pick up where you left off without having to start over.