Which domain do you want to use?

A domain is your space on the internet. The same way that a physical store or an office gives your business a physical space in the world, a domain gives your business a space on the internet.

You need a domain to use G Suite because it is what allows you to send professional emails from you@yourdomain.com. Google needs to hook up to your domain in order to send those emails and allow you to collaborate with the people in your organization.