RP is just you fighting the animals not other real-life players. PvP is you fighting pretty much anything on the opposing side (Alliance/Horde), plus all the animals. Normal is in between, you'd have to ask someone else for that.
Choose PvP, in the long run, you'll be very happy you did so. Otherwise you'll be hitting yourself when you are Lv60 on normal or RP and you can't kill other players. Besides, in early levels in PvP there is no chance you'll be attacked because you'll be in your territory.
Talents basically make your character alot better and refine him in different arts. Let me get you a link, i'll edit it in.
Here is a list of sample Shaman builds. You can even create your own build there and experiment.