Make trail renderer's material

Questions & Answers
1

As it is suggested in the documentation (Unity - Manual: Trail Renderer component) we should generally use particle shaders as materials in trail renderer for having the best result.

I want to create something similar to the effect that is being shown to the example, there, but I don’t know where to start from. I did search about Particle Shaders but nothing useful came up.

So, what software should I use in order to make a texture for such a material?

Also, the documentation is not clear enough about the array of materials that can be used. Why to use an array of materials?

2

I am not sure, however, usually any material with transparent edges works fine.

3

The reason the editor allows you to add multiple materials is so you can layer them into the trail to achieve multiple effects in a single trail using different textures/shaders, which allows you to achieve pretty complex trail effects.