Your Account String
Go to the Admin area and click Landing Pages.
Copy the Account String from the Settings section.
Make a note of it for the next step.
Once your IT department has created the CNAME, go to Admin then click Landing Pages.
Click New then select New Domain Alias.
Enter your Domain Alias. The Default Page is displayed if the visitor does not put in a URL. Enter where they should go in that case.
Enter your Default Page and click Create.