I need some help understanding what I need to do on the below please, Thanks Alex
This is a fully qualified domain name which you wish to map to your help desk. Use this feature to map eg. support.mybusiness.com to computerservicesltd.zendesk.com, so your users can access your help desk via a familiar URL. The domain name listed here will also be used in links inside emails sent from Zendesk.
Once you've added the host here, you must also create a CNAME DNS record that points support.mybusiness.com to computerservicesltd.zendesk.com. Your system administrator knows how to do this.