This file explains how to configure the system when you first set it up [0]. I've just added the one I currently have set up on my dev box to Github - it's not complex by any means but has what I need :) [1]

[0] https://nixos.org/nixos/manual/index.html#sec-configuration-...

[1] https://github.com/oneEdoubleD/nixos/blob/master/config.nix