Adding a new "$something" in a template.

[Revast]

I'm sure this is a dumb questions and has been asked many times. I can't seem to find an answer.

How would i go about adding a template within a template. Like how "$header" and "$navbar" are on all the pages. How exactly would i create a new one, say for advertisements.

I would like to ad a top banner to all my pages except a few (else I'd just put the banner in the header or navbar template). I've been manually putting in the code for the ads in each page but that's getting really annoying. I would just like to add a "$ads" code in each template so that I'd only have to edit that one "$ads" template.

Thanks.