This article will explain how to link your domain to a Google App.
Log into your Google App account and navigate to the app you wish to set up.
Click on Change URL in the web address column of the General tab
Check the Custom URL option and insert the name you want to be associated with the app.
Click on the Continue button.
(You will need to leave this tab open to refer to the settings later)
Click on the Domain from the drop down box you wish to assign to Google apps Gmail. Then click on the Manage icon.
Click on the Manage DNS icon under the Advanced domain settings section .
Scroll down and input the new CNAME Records supplied by Google (From the page left open in step 2) and click the Update DNS button.
The CNAME records on your domain will now be setup to use Google Apps.
Please Note: It may take 24 - 48 hours to propagate the changes