Tutorial on how to create sub-domain in cPanel
Login to cPanel >> Click on "Sub Domains"(You can Find this under "Domain" Option)
Now you need to fill a simple form.
Create a Subdomain
Enter your sub-domain name.
Document Root: Enter your sub-domain location(If you click in box then cPanel will be automatically fill this box with correct location)
Now you only need to click on "create"
If you can't understand or still confused then please see this Screenshot: