When creating the server, you must enter at least the domain name and a description. If multiple server templates are defined on the system, you can select one from the menu - templates determine various defaults for the new server, such as the website configuration, DNS records and so on.
Under the Advanced options section you can select a different initial database name, rather than using the default which is derived from the domain name. The user and group names cannot be changed, as they are always inherited from the parent server.
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.