First thing first, welcome to Clubsnap.
Secondly, I assume you have a kit lens that you got with your dSLR. Go read up and practice often, because by doing that, you would know what lens to buy.
You can go out and buy all the sports, landscape, portrait, etc, lenses, but if you don't have the theory grasped properly, you are just wasting your money.
All the best on your journey.