The code is open source, ThreeJS is after all a wrapper to WebGL; being that it is open source it would do you good to look at the code. Also the library isn't strictly for making video games, they have a huge demo base located here

I would not do that until you at least have a bit of experience. I don't know how big it is, but if you don't know where to look at or what things do, this might be a tad overwhelming.

I don't know anything about webgl and I don't know if the NeHe tutorials are good in that regard. The old normal opengl ones are outdated as far as I know, but in the time they were of good standard, so I would think these are surely worth a look at.

There are also plenty of starter OpenGL and DirectX tutorials out there that start with setting up visual studio and such and explain in good enough details what what does and such.

Alright, here something you can do: Make your own framework, This will be the base of every exercise afterwards.

• Create a basic framework in which you can render a triangle.
• Give that triangle a color through a shader.
• Achieve this effect: http://www.packtpub.com/sites/default/files/Article-Images/4767OS_01_04.png
• Extend your framework so it supports materials in a way it's easy to re-use and support for lights so they're easy/easier to define. (this is just to make your life easier)
• Have a camera class you can traverse the scene with.
• Create different lighting models and play around with different material properties.
• Create a particle system.
• Extend the framework with a model loader (wavefront obj should do fine for now).
• Extend the framework so it supports post processing effects.
• Make the scene grayscale through a post process effect. (or when confident, make a blur)
• Adjust the framework to your liking so you can easily (re)create scenes without a lot of effort.
• Play around with different effects.
• Think of a real life scene or something from a game and try to recreate it as best as possible.

With the last point for example I tried creating an underwater scene as realistic as possible with the simplest effects possible. I studied how water and light react with one another, why certain phenomena happen (light shafts, why water is blue-ish, why it gets darker when going deeper, etc) and tried to recreate that without doing it physically accurate. There was no stopping me from doing so, but I had a deadline so I wouldn't be able to make that in time. (was a college specialization project).

You can do this with everything basically, observe and create. Figure out how certain things are done already. Skim through the graphics programming section of this forum and see what others are doing and so something similar.

The above list is by no means the golden way and I might have missed some steps in between, so for others, feel free to pitch in. But at least this should keep you busy for a while and get your experience up in a way you can figure out what you want to do next as there is always room for improvement or new techniques to try out :)

Good luck!