Customize home page

Do you mean this comment ?

<?php
	/* Include the Post-Format-specific template for the content.
	 * If you want to overload this in a child theme then include a file
	 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
	 */
	get_template_part( 'content', get_post_format() );
?>

If so, that is not specific to this theme, it’s WP theming in general, and it has nothing to do with making Page become child Page.

To make a Page become a child Page of another Page, see this screenshot below. It’s doable within Page editing window, look over to the right at Page Attribute metabox.
https://codex.www.ads-software.com/images/2/26/writepage.png

To manage its appearance in navigation menu, do it via menu management.
https://codex.www.ads-software.com/WordPress_Menu_User_Guide

I am very grateful for your help, I am new to wordpress. My site is not a blog, just a simple commercial site, and as I add a page, the contents of that page appears on the landing “home” page, which is not my intent. I wish for the landing page to have unique content, and not a running compilation of the other pages in the site. I am a bit unclear about what a “child” page is, and I am just sorting through the code and comments trying to get the landing page to be discreet. I may be completely off track in commenting on the comments in the index file. Any help is appreciated. Thanks

To achieve what you want, there is no need to edit any theme files at all. So keep theme files as they are, as original.

If not already yet, set the permalink, if nothing comes to mind, just pick “Month and Name” and stick with it, never change this setting back and forth.
https://codex.www.ads-software.com/Settings_Permalinks_Screen

Step 1
Create a Page ( not Post ), name it with something beneficial to site’s SEO. ( optional, might as well set this Page to no sidebar if wanted ).

Step 2
Create another Page, name it “Blog”.

Step 3
Setup a static front page, putting those 2 pages into dropdown lists.
https://codex.www.ads-software.com/Creating_a_Static_Front_Page

The theme also now supports static pages with blog posts with the Blog Posts page template.