As I wrote, the application has been already banned from official store but It lives on "the net".
Firstly, you have to get the victim's phone, install the app and set it up. After setting, you don't need to do anything but waiting for SMS :).
Watch the video for more information and usage -
The app has been even reported in news -
Check out the official author's page for more info HERE.
Please note the app is only for educational purposes only, abuse of this app may be illegal in lot of countries.