Space Invaders is an old-school arcade game where you have to kill all the monsters.
The aliens start out in five rows of eleven, moving left and right as a group. When they hit a screen edge, they move down, making it easier to shoot them. The goal is to shoot all of the aliens and kill them all. When the attackers reach the bottom of the screen, the game is over. The player has three lives.
The aliens fire projectiles at the player's gun to try to destroy it. The laser cannon is partly protected by stationary defense bunkers. The aliens slowly destroy the tops of these bunkers, and if the player shoots while they are under one, they destroy the bottoms as well.
Have fun and good luck!