I found my domain needs a hosting setup. When I set up a hosting for the domain, I got a document root /var/www/vhosts/mydomain.com/httpdocs
and it FTP information. I think it is just like a virtual host setup. Eventually, /var/www/vhosts/mydomain.com/httpdocs/index.php
is made running from mydomain.com
.
When I add a new sub-domain, I got /var/www/vhosts/mydomain.com/mysubdomain.com/
as a document root for that sub-domain.