What is a subdomain?
Say your domain is domainame.ltd you would like to create news.domainname.tld, this is called a subdomain.
1. Log into cPanel and click on the "Subdomain" link
2. In the box enter the name of the subdomain, for example sub. Click the "Add" button
3. Your subdomain will be set up; note that there may be a temporary delay to access it (although this is rare)