To begin with, welcome to the WebDesign forum !
No question you could ask will be ridiculed: at the end of the day we all started somewhere and I shudder to think back to my first sites...
A coupe of links to point you to resources on web page backgrounds are as follows:
A tiled background is normally your best best to begin with, since a small image tile (a square) is repeated over the entire page. The small image means it downloads faster and Dreamweaver can easily use it to cover a whole page.
Beware of using one large image for your web page backgrounds. They take ages to download and if you have descriptive text on your page the background image can often detract from it.
If you get stuck, pop back in and ask some specific questions and one of us will try and help further.
One final note, many professional web designers stay away from backgound images entirely. Many of use prefer a standard white page background with a selection of well presented text paragraphs and high quality pictures for page content.
Just a thought.
Good luck with it