Go through the tutorials from the main game menu. They give you a good place to start. There's also a GC2 wiki, but I don't recall the url off-hand, search the forums, shouldn't be too hard to find.
I was fairly new to 4x when I picked up GC2, although I had played another 4x game a bit before so I understood the idea right off. I'm not a big gamer, but I've played lots of different kinds of games, RTS, FPS, etc. 4x rates right up there for me and I might even say GC2 has been my all time favorite game.
Have fun!
