A subdomain can be used in various ways, and it's easy to do via StackCP.
A subdomain can used for things like a new website installation, test environment or another area of the site you wish to separate from the main domain (e.g. a gallery section). You can secure them using our free WildCard SSLs.
To create a subdomain through StackCP you:
You can then add your subdomain into the Subdomain box and select Create Subdomain. You're also able to change the Document Root so that you can direct the subdomain to the folder of your choosing.