"Using the ArrayMesh": better UV and indices explanation, and/or example code without indices

**Your Godot version:**
3.5.stable.official

**Issue description:**
I am trying to get my head around using ArrayMesh, but find the documentation is a little lacking in a couple of areas, specifically around explaining UVs and indices.

The tutorial says "We won't use [array index] in this tutorial." but it then goes on to give a sphere creation example that _**does**_ use indices. This means that, as a newbie to understanding this, I don't have a good example on how to create a shape without using indices and I also don't have indices explained. i.e. either I try and implement code that hasn't been explained, or I try and create what has been explained without an example to work from.

The class description page also does not really explain what indices are or how you would use them - maybe it could be improved by use of an example of indices in use?

Also, neither page tells me what to set the UVs to. I understand the basic concept that these are the texture coordinates, but not how this should relate to the surface of my object or why they are 2D coordinates not 3D (I realise this mostly comes down to my own lack of understanding on the subjects, but that's why I am reading a tutorial). I think it would be better if either the tutorial is written from the perspective of someone with no understanding of the underlying concepts, or it links to a good generic walkthrough of those topics (I haven't found one, otherwise I'd provide a suggestion).

Maybe provide an example of how to set up UVs, normals, and indices for a simple shape (e.g. a two-triangle plane)? Code examples for this would be helpful.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/tutorials/3d/procedural_geometry/arraymesh.html

Also: https://docs.godotengine.org/en/stable/classes/class_arraymesh.html