I’ve written a guide on making a map before and there are tons of tutorials in my map tag, but I’m going to make a guide for people who, like me, mostly just click stuff through trial and error or who aren’t that great at using photoshop. In that tag you can also find links to brushes for mountains, trees, castles, etc. and some information on geography.
I’ll show you how to get the effect in the above photo and how to generate different maps for your fictional world using the render cloud feature. I use cs2 to make maps. I downloaded it a long time ago, so I don’t remember where I got it, but there are tons of free versions out there if you look for them.