Some MediaWiki info:
Included pages: One way to find (and go to) included pages (template or otherwise) on a particular page. Is to open that source page in edit mode and look at the "Templates used on this page:" list.
Although that list can be a bit much at first, as it contains all included pages (directly and Indirectly included). ("What links here" is the reverse)
Templates: Are just like other normal pages. ("templates:" namespace is there for organizing purposes)
Ie: Personal templates (like for experimentations) can also be placed and run from ones user-space. (Just make sure the call contains the proper namespace)
... Fun/Advanced stuff: Self calling pages are also possible (one recursion-level only though)