Seeing it as a first, I you're off to a decent start. I mean the sig is crap, but that's because this totally new to you. I can see you messed around with a background a bit. Don't be afraid to experiment. You can always delete the layer if it doesn't work out the way you wanted

Best advice is to go look up a bunch of GIMP tuts. Find out aboutn layering, blending, and effects