A walk in the park
This is an excellent tutorial series by Joshua Gilman in the form of The Standard Book.
It is ideal for people with prior Nix and Nix Flakes experience.
They are written in a way that feels like a walk in the park, hence the nickname.
They are also often used to dogfood some new std functionality and document it alongside in a palatable (non-terse) writing style.
Enjoy!