Quite simple; just use the mouse. Move it left to move left, and right to move right, click to fire. Don't let the space invaders hit the edge! Afterwords, submit your Wave in the comments. It gets a little harder over time! At waves like 13 or 14 it's impossible. So yea. See if you can get there. I made it very similar to the original Space Invaders, but if you want you can click see inside and switch it to left and right arrow keys by modifying the scripts a little bit.
Credits to the original Space Invaders for game idea. Credits to the creator of C418 for the song Moog City. Or something like that.. I'm not *exactly* sure what the name is.