These instructions were correct at time of writing. Things change quickly with this technology, so get in touch if you need any extra help.
1. Select the Apple logo > System Preferences.
2. Select Internet Accounts.
3. In the Internet Accounts panel are email and social media account types that are compatible with the Mac. Select Google.
4. Select Open Browser when prompted to do so in the drop-down window.
5. Enter your Google account name (email address) in the window that opens and select Next.
6. Enter your Google account password and then select Next or Set Up (depending on your OS version).
7. The drop-down panel changes to display a list of apps on your Mac that can make use of your Google account. Select Mail and any of the other apps, then select Done.
Your Google email account is now automatically set up in the Mail application.