Hi AzureIsland and welcome to the Guild.
To answer your question, I would say the majority of guild members use either Photoshop or Gimp, with a smaller number using Campaign Cartographer or other image editors like Krita or Paint Shop Pro. If you can afford Photoshop, great! Otherwise,
download Gimp for free. There are tons of Tutorials for Gimp and Photoshop, and not so many for other software, so it may well be worth while trying one of these applications to start. Take a look at
this comment which contains tons of useful info on how to get going. You can also
download PDF tutorials here to try out.
If you've never used an image editor like Photoshop/Gimp before, I'd suggest heading for YouTube and watching a few Beginner/Intro vids just to get a feel for the software and the basic tools. Both applications have layers, layer styles, filters and all sorts of other things!
I hope that's useful and look forward to seeing some of your work.
