Some Sites SOS website templates come with empty, placeholder external social page links in the navigation, horizontal and vertical (sidebar). Currently, there is no way to add an address to those links. They must be deleted first, then the link re-added. They have been placed there to let you know that you can use them.
If yours did not come with these links and you want to add them, ignore the instructions explaining how to delete them and read the instructions how to create them instead.
The process to both delete and create links to external pages is the same for both horizontal and vertical (Sidebar) navigation. The only difference is the method to get to the navigation dialog box to do so.