Need to learn programming. That's the raw truth.
GDScript is similar to Python, so:
https://automatetheboringstuff.com/
Or Python tutorials in youtube.
You'll need to understand:
Variables;
Operator:
Flow of control;
Data types;
Data structure;
List (arrays);
Dictionary;
Functions;
etc..
The Automate the Boring Stuff with Python is a good start. The book is right at the point and free to read in the website.
After that read the Godot Docs & the API. It will become a lot easier and clear how to use GDScript.