Setup

Run ./nix.sh first-time-setup
Change the secrets to the ones you use in Users/WickedWizard/secrets.nix
Change the programs.config_dir defined in System/HP-Laptop/configuration.nix to the values you want.
Change the flake details in System/HP-Laptop/Misc/autoupgrade.nix
You're done (hopefully!).

Resources

MyNixOS - All in one alternative for nixos.org

Noogle - Functions for Nix.

Hound - Search almost every known Nix repo for documentation.