Help with Story Layouts

I am really kinda confused on how to make the story layouts. Mainly about the "background image url"
I don't understand because I put a url in and it the image didn't come up. Can someone either help me understand it, or can somebody be kind enough to make one for me...it's for a new story and I don't want to use a premade one by mibba.

Please help. I'm still a bit new. { and if you like making profile layouts too and just feel like making me one of those too, I would most definitely appreciate that}

:) Emma