To use the native Google Apps mail, contacts, and calendar apps on your Android, you need to sign in to your Google Apps account. You only have to do this once:
- Open the “Settings” screen on your device. Navigate to the “Accounts” tab and select “Add account”.
- If on Samsung, Look for Cloud and accounts, then tap Accounts
- After selecting “Google”, choose “Existing".
- Sign in with your full email address under “Email” and use your Google Apps password.
- A window will pop open asking you to agree to the terms of service; select “OK”.
- You may be presented with additional steps giving you the option to join Google+, opt in to Google Play communications, or set up a credit card to purchase Google Play media. You can choose to set these up or tap Not now.
- On the next screen you can select which features you would like to sync. The core features to sync include Calendar, Contacts, Drive, and Gmail.
That's it! You can now use Google Apps from your Android. Just launch Gmail, Google Calendar, or whichever app you want to use from your home or applications screen.