Other Resources or Guides
I'm not the first person to have made a tutorial on this. I'll link here other tutorials that I know of as well as places to learn about other things that I won't cover here.
Custom Level Tutorials
Inirdin's Light Baking Tutorial
Official custom levels README (slightly outdated)
OpenGOAL information
Official OpenGOAL Documentation
Blender Tutorials
Blender Guru's Beginner tutorial
This playlist is a great place to start learning Blender over a small project that'll teach many different parts of the software.
Official tutorial playlist. Goes more into detail into each tool instead of learning along a project like Blender Guru's one. Different ways of learning.
Official Blender 4.0 documentation
There's an insanely big community of Blender online so I won't be linking more here but you should be able to find anything you need to learn.
Talking about what you need to learn, the main skills that'll be useful to learn are:
- General understanding of the software and its interface
- Manipulating objects in "Object Mode"
- Basic modeling in "Edit Mode"
- UV-mapping and Texturing
- Lighting and Baking into vertex color
Extra things such as " basic sculpting" and " modifiers" can also be great and useful tools. For example, I made a big use of sculpting for the walls in "Crystal Cave" and the "Decimate" modifier was also a great help to lower the poly count of those same walls. There are plenty of other uses of modifiers, here's a quick video overview.