Welcome to the Guild! The collaborative effort is being reborn, but slowly. If you want results soon, by all means roll your own :-). And learn as you go has LOTS of benefits.
Trouble with a question like yours is that there's a dozen or a hundred answers, depending on what you like, and what you intend. For instance - is the world you want to build a project unto itself, or does it support gaming? Or writing? Do you have preconceived ideas you need to capture, or would you be happy to generate something with some amount of randomness? What style(s) do you like? What era are you trying to capture? Modern National Geographic atlas styles, for a modern world imply one set of tools and methods, hand-drawn look on parchment another, and few-century-back printed, even typeset work is yet another. Check out the quick-start guide to fantasy mapping in the CG tutorial section - you'll get answers as well as further questions to ask :-).
Basic you already have, if you're posting from your own computer - it's crazy what some folks have produced here with naught but MS Paint or the equivalent! Do you have a restricted budget? Such commercial $oftware as Photo$hop is very capable, and many how-tos here at the CG and elsewhere on the web will be PS-specific. But there's free software every bit as capable, with at least some tutorials available -- and sometimes one can work out say a Gimp workflow starting with a PhotoShop lesson. One consideration in favor of the most widespread commercial software might be you'll be developing saleable skills. Not that one can't sell Gimp or Inkscape abilities, but many, many web or graphics shops already *have* PhotoShop or Illustrator.
I'm partial to a sorta-minor publisher of Graphics software, Serif -- reasonably capable versions they give away as a teaser, and their full-up more recent versions are an order of magnitude less expensive than the big publishers charge. If I was starting now I'd probably pick The Gimp and Inkscape (raster and vector drawing are two separate realms, calling for distinct software... which nevertheless might both be called for in a given workflow). I'm cheap.
There - did I muddy the waters enough? :-)