This content block can be added to the footer to display pages related to the current one. The connections between pages are set in the "Related Content" section of the content builder, at the very bottom of the page, below the "Notes" section. These connections are bidirectional: if you are on the About page and set the STEM Ecosystem page as related content, then the STEM Ecosystem page will also display the About page as related content.
The display options are the same as those of the cards/carousel/portfolio content block. Unlike that content block, you don't choose particular links to add. You simply choose types of post to display, a sort method, and whether you'd like to limit the number of related pages that display.
Please see the STEM Ecosystems page for a good example of the use of this content block. Ecosystem members are listed as cards in the footer of the page.