XF 1.5 Add a custom box to xenforo

Hello all,

I am using a pixelexit theme and wanted to know if there was a global way to add a boxes throughout the forum. Essentially, I would like to add a sidebox and a header box that is global throughout the forum for internal advertising. I have a couple of banners that I would like to use that would link to some high end sponsor sites.

Can someone tell me what templates to edit to make this happen? I am new to XF so any help would be appreciated.
Great. That's what I suspected, but I guess I need to know if there is a tutorial on how to add a custom ad. Everything I see is related to google adsense advertisements.

Is there a simple code to put in that will allow me to place an ad of my own? Thanks