How do they do it?

Hi this is my first time using this forum. Hopefully I can find some answer. I am trying to figure out how the background for this website is being created.

Welcome to Sitepoint. I hope you can find useful information here and, remember to return the favor by sharing something from your experience and expertise.

That is a Wordpress site. The video is simply embedded from Vimeo.
There are innumerable plug-ins for Wordpress. I recommend you try a web search for Wordpress plug-ins.

it looks like they are using a jquery script called prettyPhoto.

Welcome… i have some developer friends, i will ask them and get back to you ASAP

Ouch, no, don’t do that. Do it like this in your style sheet:

body {background: url(images/path.jpg);}