I’ve just added a Beginner-friendly Flake tutorial to my Nix for Numbskulls repo. It’s much longer and more in-depth than the other tutorials I’ve written.
It’s very much a work-in-progress, so check back periodically for new material. I think you can be automatically notified of changes by, in the upper-right corner, selecting the “Watch” drop-down menu, then clicking a watch option.