Your domain is setup already with the zones for Google Apps. You just need to register with Google, so it will manage your mail. To register, visit:
http://www.google.com/a/cpanel/domain/new (opens in new window)
After filling out the registration, you'll be asked to either:
- Upload an HTML file to [your domain]
- Change [domain] CNAME record
The easiest to do is to "Upload an HTML file to [your domain]. Select that, and follow the directions. It will involve creating a file they said, with the text they ask you to post.
After you click "I've completed these steps", there's an optional guide.
Setting up the custom URL
You can see Google's instructions at this link. Next, login to your Google Apps Domain Control panel. On top, select "Service Settings", select "Email". The setting "Web Address", click "Change URL", and select the "Custom" option (by default is mail.yourdomain.com). Select continue, and then "I've completed these steps". The step on this page was already done automatically by cPanel.
And that's it, you should be all set up. Just wait for the zone names to propagate. If you do this as soon as you register your domain on fivedev, they will both propagate together. You can also setup the other subdomains (docs, calendar, etc), according to the instructions on their page.
By default, "mail.youdomain.com" will forward to the Google Apps login page - which is http://www.google.com/a/yourdomain.com. You can read details about how this is done at this link.
You can view the entire manual and users guide by Google, from this link here.