The full documentation for the RP2040 and Raspberry Pi Pico board can be found at the following links
At Raspberry Pi we have a very community based attitude to help. We run a very popular and busy forum where you can ask questions about any aspect of the Raspberry Pi ecosystem, including the Raspberry Pi Pico.
You can find our forums at the following link.
For the main Raspberry Pi website, see here
For the Raspberry Pi Pico page, see here
All the source code for the Pico SDK, examples and other libraries can be found on Github.