New install - do I create a virtual server for the master administrator domain?

My question is: should I create a virtual server for the master administrator domain? Or is that domain a special case because it already has default/initial configuration related to it? If I do create a virtual server for that domain, what happens to the existing configuration for that domain? Does it all work out OK? (If the hostname is mail.example.com - can/should I create a virtual server for example.com and a sub-server for mail.example.com? Or vice-versa?)

My status is:

I have a VPS for a domain, installed virtualmin fine, can login OK as root through webpage at domain:10000 (I'm calling this my "master administrator" domain?)

The main virtualmin page lists "Servers Status" for mail, web, database servers. When I look at e.g. mail config, I see some settings related to my domain. (And, I guess the webserver is partly configured because I can browse to domain:10000 to do admin.)

Currently "No virtual servers have been created yet."

thanks