in reply to Learning Template::Toolkit - have I understood?

The answer to that question really depends on what you are trying to do with Template Toolkit.

Are you generating static HTML pages, or writing templates that will have content populated by a cgi script?

tpage is just a simple script for wrapping the perl modules that generate html from a template.
ttree is similar, but works recursively over directories.

For generating dynamic content I found this tutorial helpful. I don't have time this morning to read over the devshed one, but it probably covers similar content.

Update

After re-reading your post it sounds like other people edit content documents, which you then place within a wrapper template. If this is the case then you should look at the INSERT and INCLUDE directives.

If you want to generate static pages then one of the variables passed to the template can be the name of another template . The following command would generate the template, defining the 'content_file' variable with the value 'content/foo.html': 

tpage --define content_file=content/foo.html wrapper.html >  > static-
+foo.html

[download]
And in your template: 
<html>
...
[ INSERT $content_file ]
...
</html>

[download]

In Section Seekers of Perl Wisdom