Every business needs a website, and every website needs a domain. A website's domain is the name of the site. Without domains, you could only visit websites by memorizing the IP address of every single one, which - naturally - no one wants to do.
For that reason, you can't set up a website without first obtaining a domain. But you can't pick up a domain from just anywhere, either. You must go through a particular channel to do that - a domain registrar.
But there's more than one registrar out there. So, what's the best domain registrar to go through? There's no single answer to that question because it depends in part on your priorities.