how to use google 2-step verification?

1.we will e-mail every user a google key (character string) 

2.please download the app through below links:

google store:
https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2

apple app store:
https://itunes.apple.com/cn/app/google-authenticator/id388497605?l=en&mt=8

3.specific using steps is shown on the below picture, select manual entry and paste the code into the key filed, then you can get 6 numbers