Google Authenticator is a two-step verification process for your Google Account.
On your mobile device, Google Authenticator creates a code that must be inputted so you can access your account. Google Authenticator adds a secondary level of security for your device.
Google Authenticator features auto-setup through a QR code, support for multiple accounts, and support for multiple languages.
It is a simple addition to protect your Google Accounts from hijacking. To setup, you have to enable to two-step verification in your Google Account through your Account Settings in your Google Account online.