For simple skin edits like doc_background you can refer the following pdfs
http://www.vbulletin.com/forum/entry...F-Documents%29
Alternatively when you get beyond the basics do this: Install firefox, install firebug extension, click firebug lauch icon, click inspect element arrow icon, click on element. You can find out the tag name and the corresponding stylevar. There was a detailed tutorial on vb.org as well I think.