When you buy a domain at a domain registrar, like HiChina sometimes a default website is created for you. When the registrar creates the website, they add a www CNAME record for your domain so people can get to the site by using, for example, www.yourdomain.com.
If you’re not sure if you already have a website with your domain, try going to www.yourdomain.com to check it out, where www.yourdomain.com is your domain name.
If you have a SharePoint Online Public Website (no longer available) in Office 365, and you already had a website with your custom domain, when Office 365 set up your domain to work with Office 365 email and other services, your SharePoint Online Public Website may have been set up with the URL www.yourdomain.com. This means you won’t be able to get to the original site at your domain registrar, if you have one, using www.yourdomain.com. Instead, when someone goes to www.yourdomain.com, they’ll see your SharePoint Online Public Website.