The Pimoroni Unicorn Hat comes with a handy MicroPython SDK. To use it, you need to download Pimoroni's fork of MicroPython that includes the Unicorn library, and upload it to Raspberry Pi Pico. Boot it with the button pressed and drag-n-drop the uf2 file to the disk that will appear on your computer. After that you can upload any Python script to that disk and it will run automatically if it's called main.py
.
The Unicorn library has a function called picounicorn.set_pixel
that lets you set the color of an individual LED. We take advantage of this function to draw characters using a 5x7 font. Each character is represented by 5 bytes, one per vertical row of pixels (or LEDS).
See https://github.com/Ameba8195/Arduino/blob/master/hardware_v2/cores/arduino/font5x7.h for details.