How to buy a domain name
If you don’t already have your own domain, you can easily buy one online, for example from a domain registrar or a domain reseller. You get a domain name when you sign up for Office 365, for example, contoso.onmicrosoft.com. But you may want to use a custom domain name, like fourthcoffee.com.
To set up a domain in Office 365, you must own a domain and change some of the DNS records for your domain.
After you register your domain (at a domain registrar), you sign in to Office 365 as an admin and set up your domain so you can use it with your email address and other services.
Buy a domain from GoDaddy
You can buy a domain from GoDaddy directly, or by following a link in Office 365 when you’re signed in to the portal.
Buy a domain from another domain registrar that supports all DNS records required for Office 365
If you want to buy a domain from a domain registrar other than GoDaddy, choose one that supports all DNS records needed by Office 365 services. For example, use one of the following registrars.
Transfer your domain to a different domain name registrar
If your domain is registered at a provider that doesn’t support all the necessary DNS records, you can transfer it to a different provider. When you transfer the domain, you change who you send payments to in order to renew and keep your domain name.
Request the transfer at the registrar that you want to move your domain to. Look on their website for an option such as Transfer DNS. Be aware that after they make the changes, it can take a few days update across the Internet.