In simplest terms, a domain name is the name of a resource on the internet, for example, a website. These resources need to be universally recognised in order for resources to be identified, found and connected to. There can be no duplication of domain names …each needs to be exclusive and registered in such a way that servers all around the world will know where to find your resource.
What this means in practise is that you need to register a domain name with a recognised authority and reseller.
I maintain a website at https://dougwattwebsites.com.au which is affiliated with a major supplier of IT services such as domain name registration and management.