The electrical current in Australia is 240 volts, 50 cycles alternating current (AC), so most American appliances can't be used without a transformer. Wall outlets take slanted three-prong plugs and plugs with two flat prongs set in a V.
Consider making a small investment in a universal adapter, which has several types of plugs in one lightweight, compact unit. Most laptops and mobile-phone chargers are dual voltage (i.e., they operate equally well on 110 and 220 volts), so require only an adapter. These days the same is true of small appliances such as hair dryers. Always check labels and manufacturer instructions to be sure. Don't use 110-volt outlets marked "for shavers only" for high-wattage appliances such as hair dryers. Many hotels can supply you with an adapter upon request.