Adding Wrappers—Need Help!

I am using the Template Aesthetic Azure and I’ve had a really easy time tweaking it to my liking. What I can’t figure out is how to put a wrapper on it. I think its a wrapper anyway…I want to put a table over my background but underneath my posts and links.

Also, how do I add a link bar to the bottom of my header. I haven’t figured out how to do that either. Thanks for any help!