The app code is here https://github.com/AllAboutEE/Android-App-HTTP-Helper
In the video I use an Arduino but of course you don't need one. All I do is look for the "pin=" string in the GET request from the app, then read the next character which will be the pin number and toggle that pin. Then to reply back to the app I send an HTTP request with the data I want to display in the dialog which in this case is the state of the LED.