...
Enter your travel information next to each service (Flight, Hotel, and Car Rental) in each segment's heading. Once the flight information has been entered for each segment, the hotel and car rental search fields for that segment are populated with information matching the flight. To learn more about a multi-city itinerary, see Making Multi-City Reservations.
Choosing Travel Services
Tip: To save time, we recommended that you search for a flight first, before searching for a hotel or car rental. Some of the fields for hotel and car rental searching are populated by the flight search information, and search results correspond to the flight.
...