1. What is a sub domain and how does it work?
An example of a sub domain is http://stock.domain.com When you create a sub domain with us stock.domain.com would point to the stock folder in your public_html directory. These are not forwarders, but true apache sub domains.
2. How can I enable sub domains?
Sub domains are already enabled for your site. You can set them up in cpanel.
3. WWW does not work with my sub domain, why?
When you create a sub domain you can only access it at http://sub.domain.com. You can not access it at http://www.sub.domain.com