A domain name is a website name. A website name is the name you enter on your computer and then your computer is directed over to the web hosting computer that stores that website. The web hosting computer sends the information over to your computer and you will see the site. You don’t necessarily need a domain, but it is commonly used to navigate the web.
When you type in a domain name, that information is sent to one or more computers that translate the domain into an Internet address or IP address, and they sends the information back to your computer and your computer directs you to the corresponding address.
For more information see https://en.wikipedia.org/wiki/Domain_name