Creating banner ad

Hi all, best wishes for the new year 🙂

So, I dropped off for a while, but I’m back – trying to create my site at http://www.thegreatmallofadoption.com. After a lot of messing with the header image, I finally have it the way I want it. However, I want to put a banner to the right of the image. Preferably, be able to have rotating banner ads. However, when I go to put in the code, nothing shows up. Can anyone tell me why? Is it because of the size of the header image (which was actually a logo – set to 450px × 101px)?
I know where to input the html for the banner code. It just doesn’t show up when I do.

Does anyone know how to fix this? Or if I can have rotating banners in this space with the right script?