The difference is simple as: a domain must be registered by a domain registration company and then that domain name must be hosted on the internet through a web hosting company.
When you get a guests on your website, they use your domain name to view your website. As easy as it seems, there is a process that happens from the time that the site visitor is typing in your domain and presses enter.

When a site visitor enters your domain name into a browser, the domain is then translated into your server IP address,  then the server sends that user to your site files, which means that their browser shows them as a typical web-page.