@jguzz24You can use any name you want. However, you should register the domain name you eventually choose. Otherwise you hand that opportunity to anyone who wants to harm your company. And if your company website is contoso.com, your domain name should be a subdomain doesn't serve any services like HTTPS. But that is only to simplify your DNS configuration.
If you want to know details, search the web for it. There are already dozens of articles about that very topic.