Navigation to the docs can be a bit of a struggle from the main website, so here are some quick links to things you might find useful.

The Pico landing page: https://www.raspberrypi.com/documentati ... eries.html
The Pico datasheet: https://datasheets.raspberrypi.com/pico ... asheet.pdf
The RP2350 datasheet: https://datasheets.raspberrypi.com/rp23 ... asheet.pdf
Hardware design with RP2350: https://datasheets.raspberrypi.com/rp23 ... rp2350.pdf
The RP2040 datasheet: https://datasheets.raspberrypi.com/rp20 ... asheet.pdf
Hardware design with RP2040: https://datasheets.raspberrypi.com/rp20 ... rp2040.pdf
Getting Started (C/C++ SDK): https://datasheets.raspberrypi.com/pico ... h-pico.pdf
SDK Manual: https://datasheets.raspberrypi.com/pico ... -c-sdk.pdf
Python Manual: https://datasheets.raspberrypi.com/pico ... on-sdk.pdf
The Pico W datasheet: https://datasheets.raspberrypi.com/pico ... asheet.pdf
How to connect to the Internet with the Pico W: https://datasheets.raspberrypi.com/pico ... pico-w.pdf

Online Pico SDK documentation: https://www.raspberrypi.com/documentation/pico-sdk/

Also, you may not have noticed, but when you go in to BOOTSEL mode, the mass storage device comes up and the folder shows an INDEX.HTM, click on this to go direct to the Pico landing page!