It's great to have you here. Your best bet would be to check out the tutorial section (if you haven't already) and take a look at the Gimp / photoshop tutorials there. There are a couple by RobA and Pyrandon which show you how to make a map from scratch - that might be a good place to start.
Most of us are not professionals - we make maps as a hobby, so if we can do it, then you certainly can too.
Benvenuto al nostro gruppo!