Hi Abe, welcome to the Guild.

There are a few areas of the forums that will help you locate the info you're looking for. Have a browse through the Reference Section (you need to click down near the bottom to make it show more than the last 30 days). That might help with your worldbuilding questions. For actual mapping advice, have a look in the Tutorials/How To area and see if anything catches your eye. There are threads dotted all over the forums though, so Search is your friend.

As for apps, we published a blog post a few months back that was a round up of graphics software, so have a read. Arguably, for most people, it's either Gimp & Inkscape (free software to develop your maps from scratch), Campaign Cartographer series (not free, uses symbol libraries) and Photoshop/Illustrator (generally more fully-featured than Gimp/Inkscape, but at a premium. Used to develop maps from scratch). If you're only starting out and don't want to spend too much without knowing what you're getting into, give Gimp and Inkscape a try. There are loads of tutorials for Gimp especially that'll help you get going.

If you have other questions, just ask, and good luck with your mapping!