I'm a bit lost on templates and modules meaning.

In my case, I'm using com4gis forum extension, and I'd like to have a list of forums and sub-forums on one page (I don't like the way it's done on the extension).
So shall I write a module for it ? Or a template ?
The task would be simple, just gather all forums names along with their sub-forums, display some info about them and their subforums, and let to select one of them.
The display should be customizable, of course.

I can (probably) do the php part, but I don't understand how to glue all together and if I need a template for it.