Takes a while to get used to any software...especially software as complicated as Photoshop/Gimp. Then, even when you're familiar with it, there's still an awful lot to learn about how to get your particular project done. Every map I make is a learning experience. Best advice I can give is to go and try as many tutorials as you can stomach (even if they're for Photoshop). Start doing it and you'll be solving your own problems in no time. Welcome to the Guild!
M