A fairly newb question about CSS layouts

Hi, I've been learning CSS for about 2 weeks and I can create a basic page, but I can't figure out or find a tutorial on how to have the main content area stretch with the content and always have the footer at the bottom of the page.. This is quite hard for me explain, so I've got a few examples.

Note: This effect is seen most on blogs.

These 2 site seem to have it

http://www.brandonmuth.com/
http://www.ttthings.com/

But this one does not.

http://www.therissingtonpodcast.co.uk/

I apologise if my question sounds very vague, but so far I haven't found a tutorial on it so I have no idea of what the effect is called.