You must enter your credentials on the login screen as usual.
The Two-factor authentication token screen opens.
Click the request a token link. A Token code is sent via SMS to the mobile phone registered with your user name. This Token code remains valid for 30 seconds. If you do not receive any Token code within 30 seconds, you must click the request a token link again to request a new Token code.
Enter the Token code an click Authenticate. The Home page opens.
Authy is also available as an app for Android as well as for iPhone, iPad, and iPod touch users. This comes with additional features such as an option to send the code to the user's computer via Bluetooth, provided your computer supports Bluetooth wireless transfer protocol.