How to point a Google Site to a CName?

A client has a google site that he created and he wants it to have a normal www.---------co.za URL instead of the long google sites one. I am new at Google sites and all of this and would appreciate any help I can get and please I don't understand all the jargon, so if possible speak plain English lol. We already have a CName set up for him and he has the domain. I need to know how to marry the two. Thank you.