Can the skin global config section be more self-explanatory?
Using Jamroom
"Site Index" to me means the site's index/home/main page.
Thus, the Index Activity would be the Activity Feed (Timeline) section on the site's main page.
And the Index About section is the section on the site's main/index page where you put public info of what the site is about. It's a specific Admin Blog post, technically speaking. See mine at the top of my site home page where it says "Welcome to ....":
http://fotmd.com/
The instructions when setting up a site say that you can create/show this section on your main page if you as admin create a blog post with the category of: About.
In your active skin, under the Site Index TAB, you'll see a checkbox to show/hide the "About" blog post section, where you can create a top section there where you put site welcome info etc on your site's main page. Check the box to make it show, make sure Blogs are enabled for Master adimn, then when in your profile page as admin, create a Blog post, set the category as About...and put in your info. Clear cache etc and you should start seeing ti appear on your site's main home (index) page.
Remember if you are in your skin, references to "site index" are referring to the site's index/main/home page. Activity usually = Timeline. If it says index activity when you are in the "Site Index" area- it's going to mean the activity feed (timeline) on the main page, not on a profile page.
If you are in say the jrGroup module and seeing the 'index' template or reference- it means the main (index) page listing Groups. Not the index page of the site. Etc
In your cases above, the word "index" is not a command to 'index something'....rather it simply refers to the site's Index (main home) page.
updated by @strumelia: 10/15/16 02:57:23PM