Godot Signals explained in one sentence.
It really isn't that hard to understand! You're just 'connecting' something to a script.
https://www.youtube.com/watch?v=mrN6S5lC9Fw
Guidelines for clean code. This is specifically for submitting tutorials for GDQuest, but should be a good general guideline for any team or project.
https://www.youtube.com/watch?v=FB2sqJgfqXI