Use the left and right arrow keys to move and the spacebar to fire laser blasts. The goal is to destroy all the aliens before they destroy you.
This is a working game project from Chapter 14 of Scratch For Kids For Dummies. It is based on the classic Space Invaders game, first released as a stand-up arcade game by Taito in 1978. There is only 1 level, but it would be easy to add additional levels if you wish to remix it.