Well this is something like :
1. download the plugin
2. Go to yoursite.com/login/setup
3. download from google play GOOGLE AUTHENTICATOR and Barcode Scanner (not necessary)
4. Read the barcode
5. Enter the code number
6. Done
Each time you enter yoursite.com (4.5.6.)
I may have missed something but I am sure you can do this better than me. :)