The best way to get a feel for templates is to try switching to a different one. To do this, go back to the web administration page and click Advanced Options. Near the top of the page you'll see an "Update Pages" button, and next to it a description of the current template settings, and next to that a "Change Settings" button. First click "Change Settings", select a different template from both popups, and click OK. Then (this is important!) click Update Pages. The template system doesn't change anything until you reapply templates. This button is available on both the main web administration page and on Advanced Options page.
Click Preview after applying a new template, and you'll see this page transformed. Try a few different templates on for size this way.
Before long, of course, the straightforward templates included in
the sample site will get old, and you'll want to make your own
template. The ones in the site's /_templates/ folder
can provide a starting point. Or you can just take any old HTML page
you have lying around, replace the main content with a <div
id="template_placeholder"> </div> element (or, if the
layout puts the content into a table cell, <td
id="template_placeholder"> </td>), and place the file into
the site's /_templates/ folder. As long as its name
ends in ".html", it will show up in the templates popup menu. (More
complex templates can have more than one placeholder, but we'll get
to that.)