Need help with a background image

Hello everyone,

first of all I just want to say I'm an absolute beginner when it comes to ccs, or building websites in general.

At the moment I'm having issues with a background image for my website. Link: http://www.kineticignition.com/
Now please don't worry about the looks, I just set up this website yesterday and took a random image for testing purposes.

The issue is that the background image overlays both the header and the footer of the website; instead I only want it to be on either side of the body content. Using firebug led me to the yt-main div class, but apparantly it's not the right one. Could anyone use firebug and provide me with some help what I should do?

Thanks in advance