Adafruit has a tutorial for using CircuitPython with the Pico board, but if you're just looking for a quick reference and code examples, their CircuitPython Essentials are very handy. If you can't find what you're looking for in either of those, you can always go deeper by checking out the CircuitPython Docs.
Shawn Hymel has created some fantastic tutorial videos for the Pico board, explaining how to program it using MicroPython and C/C++. The MicroPython Docs include a Quick Reference for the RP2 port (RP2040).
To learn more about the exciting PIO features the RP2040 offers, the Raspberry Pi Foundation made a video that introduces its benefits and its use cases. PIO code examples can be found in the Pico GitHub repository.
Our RP2040 Dev Board offers a number of enhancements that make it a desirable prototyping and experimenting tool that you would use to figure out a design before moving to a Pico for mass production/deployment. Our board has 4 layers, the 2 inner layers are dedicated ground planes to define signal return paths and improve signal integrity. The I/O lines are divided between the top and bottom layers, allowing for more space between each line, and reducing the chance of cross-talk occurring. We offer 2 additional I/O pins, 1 of which is an ADC pin. At 16MB our board has 8x as much flash storage. Our board also sports a reversible USB-C connector with 5.1kΩ CC resistors, which allow it to draw up to 3A at 5V from a USB Power Delivery device e.g. a portable battery pack or USB-C wall charger. Most importantly, our board is thoughtfully labeled, removing any confusion about the function of each pin.
Purchase a USB-A to USB-C cable here: Red Silicon USB-A to USB-C Cable