Lol, don't worry I was like that too.
I will explain more clearly ok?.
1. go to edit signeture in your CP.
2. press on the yellow Icon that say (insert image) when you stand on it. press.
3. a small window will sppear, past the Url in it, and press ok.
you should have it.
EDit: Ren's way is alot easier.
