A great introductory book on programming the RP2040 micro controller is freely available on raspberrypi.com.
Make sure to have a current version of Python installed. Then install Thonny, either via
pip install --user --upgrade thonny
or follow the instructions on thonny.org.
If you don't own a MicroPython compatible device and still want to practice, you can use the Wokwi RP Pico simulator.
Raspberry Pi Pico (RP2040)
To install MicroPython on your Raspberry Pi Pico, follow the relevant instructions on raspberrypi.com.
Raspberry Pi Pico Pinout (svg), Raspberry Pi Pico Pinout (pdf)
A series of small introductory examples is available on https://gitlab.com/senarclens/micropython-examples/. Ideally, clone the repository via
git clone email@example.com:senarclens/micropython-examples.git