Q. READ THIS BEFORE SETTING UP A SUBDOMAIN!
A. To create a sub domain cpanel asks for the name you wish to use. MAKE SURE the subdomain name you give it doesn't have a folder already named that name. If it does the sub will not work. Example... I want to create the subdomain test.billyhost.com so my sub name is going to be test. If I already have a folder in my ftp named test I need to delete it or rename it to something different before I create the subdomain with the test name from cpanel.
Q. What is a subdomain?
A. www.domain.com is a domain name. A subdomain is anything that replaces the www in a domain name.forum.aol.com is a subdomain. www.forum.aol.com is not a subdomain.