Note : A subdomain can be seen as a second domain with a new website, new content than your main domain. For example blog.mydomain.com is a subdomain of mydomain.com. .

1) Login to your cPanel control panel

2) Click on the "Subdomains" icon as indicated in the screenshot below. 

3) On the next screen, you may type the subdomain you would like to create. From the "Domain" dropbox you may select the domain you would like to create a subdomain for and in the "Document Root" you may type the folder of your web hosting account you would like your subdomain to redirect to. 

4) Once you are done with your settings, you may click on "Create"

That's it! You have successfully created your own subdomain and you may replicate as per your subdomain plan allowance.