I've created a folder for each youtube video that has relevant source code. Feel free to download and change anything. I'm not sure how to license stuff out but I'll get to that later (soonTM). No promises that this code works with the current version of Godot but the concepts should still be applicable.
- Download the folder for the project you want to run
- Download the latest version of Godot Game Engine
- Run Godot
- Click "Scan"
- Navigate to where you downloaded the project and select that folder
- Hope your new version works with what I did ;)