Welcome!
Thanks for reporting the out dated announcement. Most of them are still valid, but not really new any longer. I've cleaned the scenery forum so it should hopefully be a bit clearer now.
Regarding your scenery question. Airport layouts (runway, taxiways) should be send to X-Plane's database at
https://gateway.x-plane.com/ Altough FlightGear uses that database, our scenery is very infrequently updated. Luckily there's some work being done to change that in the (hopefully near) future. If you want to enjoy your new scenery straight away you'll have to compile the scenery yourself. That's a somewhat more involved process, explained at
http://wiki.flightgear.org/Using_TerraGear This also applies to changing the terrain itself (landclasses, elevation). Another option for the golf course is to use
regional texturing. That will have an immediate effect and does not require re-compiling the terrain.
As you can see, adding buildings is by far the easiest option. You can submit objects to
http://scenery.flightgear.org and they'll appear in FlightGear (if you use TerraSync) within a couple of days at most.
Cheers,
Gijs