Someone else can cover the 500 mi minimum, but "actual" will depend on the flight(s). Multiple flights each having individual flight numbers should earn mileage per segment. "Direct" flights - making a stop but keeping the same flight number - generally earns only N/S miles/segments. And of course, actual N/S flights earn the N/S miles/1 segment.
NOTE - some UA "express" flights don't earn anything and are the subject of another thread.
Jim