External links are essentially browser bookmarks - simple links to arbitrary URLs along with a name and optional description. One key difference from a browser bookmark is these external links are globally available. Only an admin can add/remove them so they are intended to be used when an admin wants all users to have the exact same set of links.
To view/open external links (with the proper permissions) the ExternalLinks.getLinks permission is needed, which is available in the ExternalLinks.apiread role.
Figure 1: IAP Bookmarks
For more information on using external links, see the IAP External Links admin guide.