Sign in with your Google ID so that information associated with that account automatically syncs with your LYF device. You need to have an account set up on your device if you want to get apps from the Google Play store.
You may need to choose "IMAP" or "POP3" if you want to access your email with a program like Microsoft Outlook or Thunderbird, even when you aren't connected to the Internet.
Follow the on-screen instructions. As a security measure, you may need to enter your device's pattern, PIN, or password if you're adding additional accounts on the device. This ensures that only you or someone you trust is adding an account to your LYF 4G mobile device.