This template automatically displays a documentation box like you are seeing now, of which the content is transcluded from another page. It is intended for pages which are transcluded in other pages, i.e. templates, whether in the template namespace or not.
This code should be added at the bottom of the template code, with no extra space before "<noinclude>" (which would cause extra space on pages where the template is used). The parameter can be used as shown above to transclude an arbitrary documentation page.