You have two sub page templates to choose from.  

1. The "Subpage Default" displays your page with a sidebar and a sidebar navigation.
2. The "Subpage Fullwidth" displays your page with no sidebar and full width sections.

Your template "Subpage Default" is your default page template and the "Style Guide" page has been setup to display your site default styles.

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

The current page title will always show in the content area with the parent level page title displaying as an overlay in the header image area (unless the page header text is used).  If you are on a page that is the top level in the navigation tree then the page title will display in the header image area only.

Related second level navigation items will display above the content.  If the page is using the Subpage Default template related third and fourth level navigation display in the sidebar.