This is a simple arcade game. You are on the planet Spectra with your spaceship, Thrusta 1, and you push boulders off platforms to squash the monsters hatching out of the eggs at the bottom of the screen, while avoiding the lethal guards. There are eight monsters to a screen, and about 10 different screens, all with the same pattern of platforms but different monsters and guards.
I thought at first that the game had a serious bug, because the guards appeared and the eggs started hatching, but there was no sign of my spaceship. However, when I pressed Return the game re-started complete with a spaceship, which was a great relief.
It's quite good, but not particularly difficult, so it's more suitable for fumble-fisted amateurs than arcade aces. You start off with three lives and earn another for every three screens you complete, which is enough to keep an expert going until terminal boredom sets in. If you find a lot of arcade games too difficult though, take a look at this one.