To add your Gmail account to Mail.app, first launch the app, and (if it does not prompt you to add an account), go to Preferences, click on “Accounts” and then click on the “+” at the bottom-left corner.
Mail.app will show you various options for different mail services. Choose “Google” from this list:
Click continue, and you will be asked to enter your Gmail username (CDNIS email address) and password. These were sent to you by email.
Click “Sign In”
If you are using the account for the first time, you’ll be asked to change your password.
Next, Google will tell you what “OS X” wants to be allowed to do:
Click the “Accept” button (note: the button will be greyed out when the window first loads, but should become active after a few seconds).
Last but absolutely not least, select the “apps” that you want to use your Google account. If you will be using your Google Calendar, be sure to check that box as well.
Once you’ve done those steps, Mail.app should be automatically configured to send and receive email from your Gmail account.