To understand the difference between a subdomain and domain let's have a look at an example:
Example of the domain: example.com
Example of the subdomain: forum.example.com
Domain name consists of some text and the extension (e. g. .com, .org, .net). Domain name can be registered when you sign up for our web hosting services. If you want to register multiple domain names, you can do it after the sign up using the control panel.
When you have your own domain, you can create unlimited subdomains using the control panel for free. E. g. if you register mywebsite.com, you can set up subdomains like eshop.mywebsite.com, forum.mywebsite.com or members.mywebsite.com.