There is a train which connects to the Central Station and to Circular Quay from the Sydney Airport. You can purchase tickets from the train station, or use a rechargeable Opal Card. The Opal Card is useful for anyone staying in Sydney for a few days or more as it provides discounted fares on the city trains, buses, and ferries. Alternatively, you can use the Redy2Go shuttle for door-to-door service, able to be booked at the travel desk in the airport arrivals area.