Fly through levels shooting all the aliens and bosses. Progress through levels earning power-ups and buying upgrades. See how long you can last.
Kill anything that moves. If any aliens get past you, then you will lose some health. Keep an eye out for power-ups and be sure to save money for upgrades. Don't die.
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.