Each player commands a fleet of starships, which he or she maneuvers in an attempt to conquer all the stars in the galaxy. There is nothing to download. Games last for three weeks, and have a fixed start and end time. There are 12 players in each game. Whoever owns the most star systems at the end of a game is declared the winner.
Most players find it possible to do well at the game playing for only a few minutes each day.
Don't let the size of the documentation page scare you. In fact, I'd recommend that you poke around in the demo game first, and then look at the documentation only as questions arise. If you've ever played any kind of wargame, I think you'll find the game interface quite intuitive and easy to use. As far as wargames go, Space Empires is very simplistic.