You got it. Yeap, OZ means Australia. And you also got that there is a non-ending list with acronyms, abbreviations and shortened words that you will need to survive in Australia. There are a lot of lists you can consult. But these are by far my favorite four (the meaning is courtesy of the Oxford English Dictionary).
Oh my God!
colloq. freq. in the language of electronic communications. Expressing astonishment, excitement, embarrassment, etc.:
What the fuck?
esp. in the language of electronic communications. Used to express incredulity or annoyance:
Laughing out loud… and also Lots of laughs
colloq. Originally and chiefly in the language of electronic communications: ‘ha ha!’. Used to draw attention to a joke or humorous statement, or to express amusement.
I left them here, FYI.