Advanced Mac Tutorial

Not all videos that you encounter on the Internet will be for Big Sur, and some features/functionality shown on those videos may not pertain to Big Sur. It sounds like you are a visual learner, and yet, Apple focuses on online written guides such as:

macOS User Guide

Script Editor User Guide

Preview User Guide

Contacts User Guide

Calendar User Guide

Mail User Guide

Pages Support

Numbers Support

Keynote Support

Keychain Access User Guide

Certain Apple applications (e.g. Preview, Pages, Numbers, Keynote) allow you to place a password on a document, and there is an optional entry on that panel about allowing Keychain to remember that password. This allows you to open the password protected document without having to provide a password, as long as the protected document is in your user account. The opening application simply requests the password from Keychain.

Try Dan's Tutorials;

https://www.danstutorials.com/tutorials/

Here's a tip for Console: Ignore it. That's developer's talking to themselves. Trust me, Been using Macs since the early 90's. There is no useful information to be garnered there and but there is potential for a lot of confusion.

Script Editor: that's what you use to create and edit AppleScripts, which are a form of automation that you can do for yourself on your Mac. Feel free to google how to write Apple Scripts.

All the passwords on your Mac are stored in the Keychain. So, when an app autofills a password it gets it from there. Keychain access is your point of entry to that keychain.

Xcode is of no relevance whatever unless you're developing software applications. If you are don't expect a brief tutorial on that. Start thinking university course.