Simple question

[Carbonated_Brains]

put in the URL? (what the hell is that?)

The URL is the http://www.something.com/picture.jpg
It's an address on the internets that "points" to your picture, or document.

all I get is a rectangle witha red X......

Ask somebody on the board what the SIZE of the avatar has to be. Some of them have limits on size. If they do, you'll have to reduce the size to meet the limits.

Then just put the URL of the image, and you're there.