A CNAME record is pretty much the same as an A record however instead of pointing a hostname to an IP Address it points to a hostname. For example:
www.mydomainname.com – pointing to ghs.google.com
To set up a CNAME select the CNAME option from the drop down menu when creating a new DNS record. Put the first part of the hostname excluding the domainname.com part into the first field. Put the hostname\value in to the Canonical Name field and ensure to put a . at the end of the hostname here, then submit\finish.