The best resources I've found:
Amazing intro video by ex-NASA YouTuber Mark Rober: https://www.youtube.com/watch?v=yi29dbPnu28
To fundamentally understand what Arduino and similar microcontroller platforms (e.g., ESP32) are, what the major components of a common Arduino board (e.g., Arduino Uno) are, read this: https://docs.arduino.cc/learn/starting-guide/getting-started-arduino/
Broader Advice
Until you've chosen a specific board to get for a specific project -- such as the ESP32-C3 because it's small and supports Bluetooth, if that's what you happen to need -- then in general it seems like the Arduino Uno R4 WiFi is a good choice; I'm liking mine so far and the library compatibility seems pretty solid.
If you get a very new board then superior hardware specs may be outweighed by immature software. I'd stick with boards that are at least 1 year old.
I got an ESP32-C6 and the software support is noticeably worse than older boards.
IDE-wise, Arduino IDE 2 seems mature enough thus far. I had an issue and switching to 1.x didn't help. I also tried Espressif's toolchain and had nothing but problems trying to get it to upload compiled code to my ESP32-C6 by using idf.py. I eventually got Arduino IDE 2 to work and it's worked well since. (I had to manually tell the IDE to treat my board as an ESP32-C6 Dev Board, which it should have been automatically detected as, but wasn't!)
That's all for now. Happy hacking!