Well, according to my knowledge of games, it's a military style, real time (i hate these), scifi and strategy game. I avoid games as such, so I'm not quite sure about the details.
But here, this link may help.
http://voices.yahoo.com/how-play-starcraft-tips-beginners-452353.html?cat=2
or you could just wiki it if you are willing to read through paragraphs of intense writing .__.