Comes with simple code examples in Arduino, Python and C to get you started easily.
Here’s the manual (check your downloads folder)

What is it?
A drop-in expansion kit for the Raspberry Pi Pico microcontroller board.
It lets you use your Pico’s 2 UARTS for MIDI projects.
You can also use any of the Pico’s GPIO pins using dupont cables.

Features:

Features
powered by the Pico’s USB connection. You do not need to supply 12 volts unless you want to for a future project i.e. Eurorack.
Properly opto-isolated MIDI in as per the MIDI Association standard.

3 X buffered LEDs to indicate MIDI in and MIDI out activity on both MIDI out sockets.

Easy GPIO UART selection by jumpers with default positions shown. Default positions choose default Pico UART RX stdin and TX stdout to simplify your code.

4 X on-board uncommitted DIP switches to (e.g.) select MIDI channel, use as mode switches etc. Each is tied to ground with a 1K resistor.

Can be powered by USB alone or a choice of 12V DC input or Eurorack power.

Example code (Arduino, Python, C) provided to get you up and running.