Open Apple Mail.
Click on Mail in the top menu, and then Preferences.
This will bring up the preferences window. Select the Accounts tab at the top.
Click the + button in the bottom left to add an account. Then select Google for the type of account that is being added.
Enter in your full email address.
Enter in your password.
Select what you want to synch (probably just Mail) and click Done.
That’s it! You should now see the new account in the Mail app.