Well, there is a set of things you need to do.
Sign up with your google apps account.
You will have to then point your MX records in your own control panel to the google's mail servers.
Validate your website.
Create a list of your users for using google apps. This will include your domain emails.
Be sure to to catch all mails to: receive junks or not to lose any emails.
Forward your new domain account to your personal gmail if you like. If so, also:
Go back to your gmail account and add a new email sending account within gmail and verify.
Now, using your own personal email address, you can interact with the web-site's email address, without letting people know what you are doing in the back for your comforts. If you want to use more than 50 accounts you have to purchase the google apps.
And, if your control panel stops forwarding your mx records, you will be back to your server's emailing services.
Also, with registrars like godaddy, you can directly point the mx records to the google, instead of having to come back to your hosting first.