The main support for the Pico running the u2if firmware in Blinka utilizes the hidapi library. Some of the features rely on sending data via a serial connection. For that, we use the pyserial library. And to allow use of CircuitPython Libraries, we need the Blinka interface layer.
All of these in turn rely on a several other things which vary for different OS's. So before we can actually use the Pico, we need to get everything setup. See the OS specific sections for what we went through to get things working for each.
Just for reference, here are links to more information about the main Python libraries being used. Here's the README from the hidapi source code repo, which has some install information:
Here's the main documentation for pySerial:
The pySerial source code repo is here.
But first try the install instructions on the pages that follow for your OS.