The electricity supply in Australia operates at 230 volts / 50 Hz, the same as in the United Kingdom. However, the wall sockets are different and an adapter is needed. See image below:
Visitors from other continents should bear in mind that if the supply in their country is lower (USA and most of the Americas operate on 110 volts) their electrical appliances will not work in Australia safely. Using a 110 volt appliance where 230 volt is supplied can damage the apparatus and cause a fire; you would need a voltage converter, not an adapter!
Having said that, nowadays, most travelling appliances accept a wider range of voltages, from 110 volts to 240 volts, therefore, being adaptable to most countries' supply. So, check carefully the voltage stamped on the device before plugging it into the socket.
If you are travelling from a country with a different plug/socket type, you should take a travel adapter with you to enable you to plug your electrical devices into the available wall sockets, once you arrive in Australia. However, most hotels, especially those from the higher categories, will lend you an adapter if you forget to bring it with you.
In any case, most good hotels provide hair-dryers, and irons on request; so you can leave yours at home.