Almost every form of public transport in Sydney uses a pre-paid system called the Opal card. Opal cards can be bought at most newsagents and 7/11 stores, and start at AU$10, but we suggest loading more money on the card if you want to do any sightseeing or to take the train to the Airport.
Unfortunately, concession rates are only open to NSW students, NSW pensioners and children under 16. We highly recommend purchasing an Opal card if you want to avoid being yelled at by local bus drivers.
Thankfully, the Opal card can be used on buses, trains, and ferries throughout NSW, so this will allow you to visit popular tourist spots such as Circular Quay, Bondi Beach, Manly, Taronga Zoo, and Cockatoo Island.
Find an Opal card retailer here: http://www.retailers.opal.com.au.
For more information, please visit: https://www.opal.com.au/en/about-opal/opal_for_visitors/.