Setting up the parallax background?

My website looks like this: http://gyazo.com/53d2cabd846c5991f20aadc1a228fd64

I am trying to get it to look this this: http://gyazo.com/0b871c81f30588064d394abd525925e5

The “content” is sort of in the middle of the screen, if you know what i mean.