Background Image for Forum

I want to have a certain image for the background in my forum and I don’t know what to put in the box beside “Background Image:” Do I put a link to the image, what?
And also I want to put a header and where do I put that?

Yep, you must put a full path to the image to the box. ( etc.)

Max discounts with [color=#CC0000]E97[/color] or [color=#CC0000]O97[/color] code. U will never find better one. Check it and U will see!
Webhosting infos, who sucks, who oversells?

Can you give me steps as to how I do it? Please (:
And do you also know how to put a banner?