Hey all, new to this site but i was wondering if anyone could help me (with what i think is a simple problem, but has been driving me up a wall)

How do i make something similar to this:

http://bespokecouturenyc.com/

(after you enter the site the background images change regardless if you click a button or not)

I've searched google for about 2-3hours for tuts on this but with no luck, help me FK help!!