You could pick your crew (there was a grashopper-like dude, a robot, humanoid, etc) and then your job was to collect various minerals to be used for fuel on your home planet.
You could analyze a planet before you landed, cheking the levels of oxygen and the weather conditions before landing. You could probe the planet to check if it had high levels of certain minerals, etc. Also, you could be attacked by various life forms and even killed.
The graphics were virtually non-existant, but the game really was great exercise for the brain.
It's a "build a civilization" kind of game. You start out with some workers, they build buildings and collect resources to advance you to the next age of civilization. Empire Earth is pretty complex in that you can advance through 13 stages of civilization, from prehistoric to cyber-technology.