Omeka S allows users to build multiple sites per installation which are not necessarily connected. However, each installation has, by default, a front page which lists the sites in the installation. This page is accessed by going to the main url of your Omeka S installation; if your [admin dashboard] was at yourdomain.net/omekas/admin, then you would find this page a yourdomain.net/omekas/

The page displays all sites which a user has permission to see, along with the site's summary if one exists. If someone is not logged in, they will only see public sites. A logged in Global Admin, by contrast, would see all existing sites on the installation.

Installation front page for the "Stackable Sandbox" showing seven sites, three of which have summaries.

If you want this site to be hidden from site visitors, you can use the setting Default Site to select a public site on your installation to which visitors will be redirected when they navigate to your base url (yourdomain.net/omekas/)

You can use the Default Site option in conjunction with the site page block "List of sites" to create a branded site index and to add an about page for the overall installation.