Not sure if it's beginner friendly but I found implementing NeRF from scratch a good exercise. Especially since it reveals many details that are not immediately obvious from the paper.
I've been working on implementing this too! It's been fun trying to debug problems by figuring out how to reduce it to the "bare minimum" to repro. Ex: does it work if I disable positional encoding? Does it work if I have only one sample per ray on a single image dataset? Etc