Using CSS to make ummm

Alright im not sure how im going to go about explaining this but ill try…

Iv just started using CSS in my sites, and now that im actually working on my main site i need to use CSS on it, anyway the problem is that I was wondering how you can make it so that the site can extend to the bottom of the browser? so that no matter if i use a diff screen resolution or use my browser fullpage then it will still just make the page goto the bottom of the browser so theres no gap between the browser bottom and the site…?

IF anyone could understand what i just said and can help, would be greatly appreciated…Ben