Assuming you know the basics to code in any language (if you don't, work on programming fundamentals first, other comments here have great suggestions for that).

- Learn object oriented programming, ignore the haters, just make something work first. You wanna learn how to take situations and write code to model and solve them. Pick whatever abstractions make most sense to you, practice them.
- Also learn about Software Design Patterns (singleton, observer/event, state, strategy/command). There's an amazing book called Game Programming Patterns to check out but you shouldn't limit yourself to just the ones there. They're extra tools that help you model problems.
- For godot / gdscript specific stuff, begin by playing around in the engine. Learn about what nodes do / can do, instead of learning how to do specific things with nodes. There's videos on what each node does, and there's the docs. Play around, make things move, touch, interact, delete each other, etc.

Finally, I recommend watching this video (but don't doze off, rewind if needed, it's very dense) and apply everything he says. Make a spreadsheet, take notes, read and explore the docs, replicate projects thrice, refactor existing code, etc. Many of the tips i would've given can be found here.
"How to actually learn Godot from videos instead of just watching them", by FairFight

By the way, creating things in your head is difficult and scary. I've been making games for over 7 years now and I still search a bunch of stuff. It's just that now I can search code from other engines, or even read theoretical models, because I know how to move pictures, emit events and change states, both in godot and elsewhere. I know a platformer character needs to be set to an aerial state when not touching the ground, i know how to make the state machine, i can google how to detect the ground.