Great that you have planned to travel to Sydney, Australia. Sydney is a great place to travel with major attractions like Sydney Opera House, The Harbour Bridge, The Rocks, Darling Harbour, The Royal Botanic Garden, Queen Victoria Building and many more.
Here are few things you need to consider to avoid getting into any trouble.
When you arrive at Sydney Airport you must complete an incoming passenger card and clear customs. Australia has some of the most stringent customs and quarantine regulations in the world – it is important that you know which items you cannot bring into Australia and which items you must declare to as there are severe fines and penalties if you do not follow the rules.Weapons and firearms and illegal drugs are prohibited in Australia. Restricted items must be declared to a customs official. These include large amounts of currency over AU$10,000.00, prescription medication, food containing animal or plant products, plant items or wooden items.
For more information check out the Arriving Travellers section of the Australian Government's Australian Customs and Border Protection Service site.