You're a mercenary and you're living on planet Rokilot. You receive your orders directly from this planet. Now you have to fight against Mutalil, a planet that has sent blue creatures to Rokilot. Shoot them all and make sure they don't touch you! You gradually receive more weapons and it's possible to get teleported, but not too often. Keep an eye on your 'Health Bar': it's shown in the green bar at the bottom right.
Use the arrow keys or WASD to move around. Use the mouse to aim and to shoot. E or Spacebar = next weapon, Q or Shift = previous weapon.