I have struggled with understanding Nix package manager for a long time. I use it on my macOS as a daily driver, but never understood the various pieces involved for me to comfortable make changes to my configuration. `nix-env -i` and `nix-env -e` were all I was comfortable with.

This blog post does a good job of breaking down the Nix package manager's knowledge into decent sized chunks that one can easily understand and reason about.