You have three sub page templates to choose from.  The "Subpage Default" displays your page on a full width layout.  The "Subpage w/Navigation" displays your page content on a full width layout and adds a sticky navigation to scroll between your sections.  The "Subpage w/Sidebar" displays a two column layout with sidebar sections and a sidebar sub navigation.

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