The "Subpage" is your default sub page with a sidebar, and the "Subpage Fullwidth" displays the content area the full width of the container.  The "Style Guide" page has been setup to display your site default styles.

The subpages do not include a page title by default, but the "page title" field can be used to add this in. 

*NOTE - The index.php is your home template and assigned automatically to your home page.  This templates operates the same as your "Subpage Fullwidth".