[endgame]

This article and video might be good for you, but they are more about a conceptual overview of what the fundamental parts of Nix are and how they interact.

https://shopify.engineering/shipit-presents-how-shopify-uses...

https://www.youtube.com/watch?v=6iVXaqUfHi4

Flakes are a dependency-pinning and hermetic evaluation feature baked into the Nix tool itself.

Overlays are an idiom that uses lazy evaluation to build up larger attribute sets in a modular and composable way (e.g., package collections for a particular programming language).