It's your classic space fighter game, obviously taking place in the distant future where space travel and other life is not a new thing. You're a pilot in the middle of a war and you learn controls for your space fighter and you can customize weapons and stuff (you get training mission too). Out of the blue, your species (Terrans) and the enemy specices (Vasudents) are attacked by another alien species and you and the Vasudents must ban together to survive.
http://en.wikipedia.org/wiki/Freespace

It also has a sequel where everyone has shields and new weapons and more challenges.
http://en.wikipedia.org/wiki/FreeSpace_2