@Jenkler IMO the best example is their code!
You could replicate and modify what in NodeBB are categories as groups (Movie/games/tv show), and what in NodeBB are topics as actual elements (a movie, a tv-series, a game). The best examples of code are their one and you can find them in /src
In order to use these things in your plugin, check official plugins code ^^
In my opinion is the best way to learn