NixOS and Git- I am noob

Hello all, I just installed NixOS over a Kali build on a good ole’ T420 laptop.

Noob nixOS context:

My first foray into NixOS and added just one app to the etc/nixos/configuration file, and then the obligatory “sudo nixos-rebuild switch”. I don’t know much more about nixOS.

Noob git context:

I’ve dabbled with using a bitbucket repo to host some configuration files, using commands on windows git such as:
git init
git remote add origin https://blahblah
git status
git add
git commit -m “Message”
git push
and editing a .gitignore to be useful

I am struggling very much to understand the vast delta between that knowledge and getting something like this Kali’ish NixOS build hosted in git to work:

I feel this video gets a lot of that delta wrapped up, but not so much for all the additional files the git repo has.

Or after setting up git, is it really as simple as adding all of the .nix lines like so?

Or better yet go full deluxe and all listed in the link mentioned in that post?