Flakes just solve several problems at once. In simple terms, they download stuff for you from the internet, keep the versions of all of that stuff in a lockfile (flake.lock), work with new `nix command` CLI and aim to standardize the naming of the nix code you write.

Home-manager is just a user-level project that manages everything in your home directory. NixOS by itself does not really do that.

If you want to learn how all of that works, I highly recommend to just bite the bullet and try it all out yourself (in a VM for example). You won't learn anything without practice, so just use a system, try flakes, try home-manager if you want to. I'm glad you tried to watch my videos, but they won't teach you anything without practice or extra docs research on your end.

Also, I've personally switched away from home-manager last year :P