The related content block has 2 modes you can toggle between using the "pick related content items" switch.

The manual select mode allows you to select the internal pages, external links, and documents you want to link to using the LINKS property

The list mode lets you choose between child items or siblings using the radio button to select

Both modes can be displayed as "lozenge "blocks or a list of links.

Hidden toggle: shows/hides block

Background colour: Adds a background colour to the whole block

Navigation title/Anchor: creates an anchor link that you can use to link to from a navigation object e.g. url#anchorlink

CSSClass: you'll not need to use this

Remove gap: Remove the top padding from the block so it sits tight to the preceding block.