creating a subdomain site?

In trying to further troubleshoot my problems from my other post, I decided to do it one step at a time and keep it simple.

What is the proper way to create a sub-domain virtual server with its own ip?

Here is what I did, but when I visit the site I create it doesn't work. Can't even ping the site.

1. click on an already existing site in my virtualmin panel
2. click on add virtual server and choose sub-server
3. in domain name box I type in 'xyz.primarysite.com'
4. server configuration file and account type are both default virtualmin dropdown choice
5. network interface I choose virtual with ip and assign a new ip address assigned to my server
6. click start

When try to visit either the subdomain.primarysite.com or the ip address I assigned I can't reach the site.

Is there a step I might be missing?