Welcome!
I suggest you check out the release and tutorial sections. A great source to start with are the ones from Ketchup. I suggest you try the v15 'clean' source first. Ketchup has released the v15 source for Visual Studio 2019
here.
Don't try to just add new features to the source. First try to understand how the source + resource + client work. Edit some small things and see what it does.
If you need any help, just add me on discord (check my signature). I'm not going to spoon-feed you everything (No remote support). There are a lot of tutorials on how to setup the server files (RageZone + Youtube).