Start: Begin by choosing your game engine! You MUST choose a text based engine, I'd recommend using Unity, Godot (My choice!), Unreal, or Game Maker Studio. Engines such as Scratch, GDevelop, or Construct 3 are unfortunately not allowed.
Next you'll want to come up with an idea and begin your project! I'd recommend writing down your ideas on a google doc or figma page before starting, but make sure to keep your idea SIMPLE, you need to finish it and the scope is bound to grow over the course of it's creation. Open up your editor of choice and start a new project. Here's a few guides for the engines I mentioned above:
Unity:
https://youtu.be/hKXsL7XNa9M?si=e-flrrwnGjE5U5bdGodot:
https://youtu.be/5V9f3MT86M8?si=DUYqai9KYJc9NbPqUnreal:
https://youtu.be/dS5AUaYFcdw?si=Ks7V1a1xCp1gk_8aGame Maker:
https://youtu.be/a9f4QdHGM4k?si=67FRQYhWq02UFV0G