A subdomain name is like a "Domain within a Domain" that can be added to any domain on your account. For example, a subdomain of whhsupport.com would be wordpress.whhsupport.com.

First, log into your account cPanel and click on "Subdomains" under the "Domains" sub-header:

Under "Create a Subdomain," add the subdomain that you want to add.  It will automatically be given a Document Root, but you can change it if you would like.  Once that is done, click on "Create":

Now you can verify that the subdomain was created under the "Modify a Subdomain" section: