Google has provided tutorials for common email clients.
- For Outlook use http://mail.google.com/support/bin/answer.py?hl=en&answer=77689
- For Apple Mail use http://support.google.com/mail/bin/answer.py?hl=en&answer=180188
- For other email clients, use http://mail.google.com/support/bin/answer.py?answer=75726
