Under the Advanced options section you can select a different administration username, group name and database name for the server, rather than the defaults which are taken from the first part of the domain name. A contact email address for the server can also be entered - ideally this should be the existing address of the person who will manage the server, in a different domain.
To select which features are enabled for the server, use the checkboxes in the second part of the Advanced options section. Some features depend on others and cannot be selected on their own - for example, Webalizer reporting on website statistics depends on actually having a website.
At the bottom of the Advanced options section you can select to have all web traffic to this new site forwarded to another URL, and to have all email forwarded. You can also select to have the new virtual server use its own private IP addresses, which is required for SSL and anonymous FTP hosting.