Yea it's definitely a jungle haha, it also seems they're changing things up a bit with where the most recent docs might be hosted

https://search.nixos.org/

so, if you searched for vscode in that link, then click the "NixOS Configuration" button, you can see

  environment.systemPackages = [
    pkgs.vscode
  ];

or if you're using the with convention to factor out the pkgs object/contextual keyword(not sure if that's the right name)

  environment.systemPackages = with pkgs; [
    vscode
  ];

for zsh, just having this in your configuration.nix should work https://nixos.wiki/wiki/Command_Shell

programs.zsh.enable = true;
users.defaultUserShell = pkgs.zsh;

Again, these values should be inserted after the function definition of your configuration.nix

{ config, pkgs, ...}:
{
   # Things get inserted here typically
   imports = [ ./hardware-configuration.nix];
   environment.systemPackages = [pkgs.vscode];
}

for example.

Something I've noticed from developing on nix, When the headaches of nix appear, the solution might be harder, but I usually end up with a better solution than what I was going for before. Some examples:

• My resume is compiled in Latex. I tried the pdflatex package in nix but it gave rendering issues. Then the nix community recommended tectonic and i'm getting better compilation times, logging, clean up...

• PIP is a garbage package manager, and it's garbageness sometimes makes native python development a headache in nixos. However, using poetry2nix, not only could I define development environments, it was also ready for packaging on PIP

Sometimes you might want to separate some parts of your configuration away from your global system config at /etc/nixos/configuration.nix. That's nix-shell, nix-develop, nix-build, and flakes are for. I'm not a pro at flakes yet, but I think I got the gist, here's an example of when I wish I could have used a flake:

I use discord but discord itself is garbage. Vesktop is a better 3rd party client for discord. Unfortunately, I had to remove it from my configuration.nix the last few weeks because one of its dependencies wasn't packaged right, causing my entire system to not build. If I had used a flake, I could have isolated that dependency from the rest of my build, while still tracking its integration with my system. I believe this could have allowed me to update the rest of my system, while still defining the errenous app as part of my system. Flakes are supposed to be more reproducible as well, since they require sha256 git commits, whereas other package managers only ask for a subjective version number

There's a lot to learn with nix but even if I don't stick with it long term I feel like It's making me a smarter software engineer since a declarative/functional paradigm tends to match the natural language more. It also is the most restrictive design paradigm, which means it's brief but so simple it can be hard to understand as a consequence. Since it's so restrictive, it's also a subset of all other paradigms. You declare what you want, ideally, you don't have to set anything up. I never had an easier time getting cuda drivers for ML Training setup than on NixOS because of this

Something I enjoyed doing, was setting up my user profile to let me ssh in only with whitelisted ssh keys, as well as setting up a systemd script to handle some start up routines on my OS. I think that can be a gentle introduction to how you can configure other parts of your operating system. I'm going to try and set up a CI/CD/CT pipeline with it next I believe

Edit: The next thing I need to do as well, is consolidate my user configs with the home manager functionality. I use a KVantum Theme engine on top of plasma, and while those apps are installed in my system, the configuration of which theme to automatically load should be integrated with the text config aspects of nixos. Currently, I "Imperatively" configured those by "Opening the app and clicking", which will get erased/not be reproducible if I ever rebuild my nixos on a new computer

Another funny thing with functional programming... sometimes the fix is as simple as

sound.enable = true;

Even though I had pipewire enabled as a service and everything, that one line needed to be there haha