That is where you start!
Rebuild that demo-plugin, preferably without looking (too much: ) at the code.
Understand the code!
Understand the 3 layer-hierarchi
Low-level: GTA & RD : Natives
General plugin-level (GTA & RD incapsulating Natives: RAGE
Pure LSPDFR ( incapsulating Natives & RAGE ) Functions
You find all Natives here:
https://nativedb.dotindustries.dev/gta5/natives/
You find RAGE here:
https://docs.ragepluginhook.net/
You find Functions in VS-IntelliSence after adding LSPDFR as a reference in VS
If you have any issues, ask : )