Go to Websites & Domains.
Click Add Subdomain.
Specify the following:
- In the Subdomain name box, type the portion of address that will be added to the domain name of your main site.
- In the Document root box, type the desired location of the directory where all files and subdirectories of this site will be kept. You can use the default directory of the main site, called httpdocs, or specify another directory.