Adafruit explains this very well.

https://learn.adafruit.com/adafruit-qt-py-esp32-s3/circuitpython-2

https://github.com/esp32beans/USBnunchuck_mouse

code.py is a renamed copy of nunchuk_mouse.py.

CircuitPython files and directories

└── CIRCUITPY
    ├── boot_out.txt
    ├── boot.py
    ├── code.py
    └── lib
        ├── adafruit_bus_device
        │   ├── i2c_device.mpy
        │   ├── __init__.py
        │   └── spi_device.mpy
        ├── adafruit_hid
        │   ├── consumer_control_code.mpy
        │   ├── consumer_control.mpy
        │   ├── __init__.mpy
        │   ├── keyboard_layout_base.mpy
        │   ├── keyboard_layout_us.mpy
        │   ├── keyboard.mpy
        │   ├── keycode.mpy
        │   └── mouse.mpy
        └── adafruit_nunchuk.mpy