The existing scenery is limited and only good for about a 30 minute flight, which is not very long. Scenery for Flight Gear One can be downloaded at this page:
The default scenery is w130n30
The scenery map is here:
To install, dowload the scenery file and copy it into the Flightgear/scenery folder. "c:/Program Files/FlightGear/scenery/"
Then use the back button and then the add button Fgrun to add the scenery directory to the launcher.
eg: c:/Program Files/FlightGear/scenery/
Use Atlas to display the scenery and airports in that scenery. Select that airport to start flight gear and check if the airport is really there. If it is there with runways and all, you are done. If you end up in a blue featureless ocean, something is wrong.