Of course, Australians speak English—but Australian slang will likely be a whole new ballpark for you! Don't overuse them (it will seem like you're trying too hard) but learning a few common Australian phrases in advance will have you speaking like a true blue in no time.
See ya this arvo: See you this afternoon
Dunny: toilet/bathroom
Hooroo: Goodbye
Thongs: Flip-flops/sandals