Free Orion is an open-source, platform-independent galactic conquest game in the tradition of the Master of Orion games. Its commercial competitors, just to give you an idea, are VGA planets, Galactic Civilizations and Space Empires.
Free Orion instead is a collaborative promising project, a community effort that moves forward based on the motivation and contributions of users and it is currently in the alpha stage.
Although graphics can be interesting, the game is somewhat difficult to enjoy for new players. There is little in the way of guidance and at the beginning, FreeOrion appears rather boring.
In theory, victory is achieved by eliminating all ships and planets belonging to other empires, that's fairly standard, but at this stage there isn't any combat yet.
You must read the 'quick' play guide, (which isn't that quick) in order to understand a bit what to do. The guide starts in a very step by step way: 'to start a game, run the freeorion executable, then click on the 'Single Player' button on the main menu, then 'OK' on the Galaxy Setup screen.
You should then see a starmap which you can drag around with the mouse and zoom in/out with the scrollwheel. The triangle next to the star is a fleet.
Clicking the fleet opens the fleet window. Try moving fleets around to explore, making a new colony or clicking on techs in the Research screen to read their descriptions.
If you are patient enough, and you are really passionate about strictly strategic games you might want to try this project and maybe collaborate in the related forum for further, more exciting releases.
As specified in the game's Wiki, the easiest way to contribute when new to the project is simply to join in brainstorming discussions on the forums.