Configuration (Wizard step 2)
After the installation, you can set your domain name at https://example.org:81/app/network
This depends on your topology.
You may need to add an A record of your *. FQDN or your *.domain in your DNS. DNS management is typically offered with your domain name registrar, but you can also use a specialized service.
Below is an example with Gandi.net, where everything (mail, XMPP, web, etc), and all subdomains (ex.: conference.example.org) goes to the same server.