Well you are certainly in the right place to learn how. MANY people (myself included) have come here looking for tips on how to create fantasy maps for their RPG campaigns. I had no experience at all, either in cartography or in working with digital mediums prior to coming to the Guild However, with the help of the wonderful tutorials here and the tremendously helpful community, I was able to pick it up rather quickly. My suggestion is to browse through the finished maps for inspiration, then through the tutorials to see what is feasible for a beginning project, as well as what software is required. Then dive right in. Look forward to seeing what you come up with.

Cheers,
-Arsheesh