biggrin dont worry there are a lot of tutorials in the internet
1.) Here's one that teaches you how to color line art in gimp(although its only until the skin, but at least it teaches you the basics)
lineart tutorial2.)Once you've grown comfortable coloring go here for tips on how to shade your pics
shading tips3.) If you need help in specific things go here
tutorial source4.) Oh, and did i mention you can download free brushes to make your art look cooler^^ here are 2 links:
brush source 1brush source 2*hope this helps^^*