Subdomains are a way of creating separate domain under your main domain, which are accessed as separate URLs.
For example, you could set up a "yourname" subdomain under your main domain "maindomain.com", which would be accessed as "yourname.maindomain.com".However, you do not create a new cPanel when you create a subdomain.
Most important : You can access sub domain URL ( Eg: https://yourname.maindomain.com ) on the internet if your main domain (eg: maindomain.com ) pointing to hosting server using correct nameservers.
