If you see a prompt to add an account when you open Apple Mail, skip to step 5:
- Open the Mail app on your computer.
- Select the Mail menu at the top, and then Preferences.
- Open the Accounts section.
- Click the + button in the bottom corner.
- Choose Google.
- Type your name.
- Type your full email address (e.g. email@example.com, or username@your_domain.com for Google Apps users).
- Type your password. If you use 2-step verification with your account, you'll have to enter an app password.
- Click Set up.
- Make sure Mail is selected and click Done.