In game you need to fend off the wave of mutants. To kill mutants you have 4 types of weapons, during the game you have to collect first-aid kits, ammo for your guns, that are scattered on the map and you'll need to shoot the eggs of the cosmic mutants in order to pull out additional ammo and first-aid kits.

If you don't shoot space eggs in time, then mutants will start hatching from them. In game you'll meet bosses of the cosmic mutants, for which additional achievements are given.

You need to go through all waves of mutants to get to a new level.