Hello, boojum! It's not necessary to be a comuter expert to work with pictures, you just need to get the right softwares, a few tutorials, and get started.
The most famous image editor is ADOBE PHOTOSHOP, used even by professionals like the Oddworld Inhabitabts artists.
You can find a shareware software very simmilar to that, called PAIT SHOP PRO.
However, I use a free software called THE GIMP. It's a simple and powerfull tool. You can find everything about THE GIMP
HERE
Just to start, read carefully these two topics:
ABE BABE's banner requests
and
Sydney's banners requests
My banner, I did it myself, for instance. But you can ask Abe babe or sydney to make one for you, if you like