No Background No Foreground

Here's my avatar, it took like 3 hours but I finally have it in layers that aren't jpg format. I don't know if anyone noticed but my old one had lots of smudge on it as the mouth moved.

Now I need someone who's good with GIMPshop to tell me how I can insert and foreground and background. I tried individually but it's all weird and messes up the black in my character.