This is an app for the Flipper Zero that emulates a game controller (specifically the Xbox 360 controller) and lets the user interact with the emulated joystick, A and B buttons. It also contains a full implementation of XInput for the Flipper Zero that supports every input that a regular Xbox controller does, which you may use in other applications.
Connect your Flipper Zero to a computer, or any other device that supports XInput. This app likely doesn't work on Xbox consoles.
From there, open the app and it should connect automatically. The D-Pad acts as your left joystick, the center button is A and the back button is B. Holding the back button by itself will close the app, but using other inputs with the back button won't. Closing the app will reboot your Flipper.
Dave Madison's "Understanding the Xbox 360 Wired Controller’s USB Data" - Detailed documentation of the protocol
Willy-JL - Help with bugs
Microsoft - Creating the Xbox itself
The Flipper Zero Team - Creating the Flipper Zero itself