The issue I see with your approach is that you’re looking for a tutorial for something that is basically infinitely flexible, there’s multiple ways to do things, etc.

By installing NixOS, you have already completed the tutorial. My advice is: Approach your configuration (which is actually code) like a static one first. That is set the values you want, maybe split up files a bit, keep it simple. At one point, you’ll get somewhere where you think that there has to be a better way to do it than just write down everything explicitly. Then, approach problem per problem. At least that’s how I did it.

Dunno if that’s the best way to do it, if you want to start managing a server farm right now that approach won’t scale of course. The issue with configurations you find online is that they’re rather complex – which makes sense for the cases these people have written them for. But for one or two machines, you don’t need to fold attributes / generate attributes from list etc. right away. If you’re not in a rush, get a feel for everything on a low level first, and then approach the deeper mechanics.