There are many tutorials out there and I can even write one up myself if the interest is strong enough. GDAX or Coinbase would be a good place to start, but I’m not sure if they have any restrictions on Australian accounts. If not, depositing your AUD into GDAX or Coinbase through a wire transfer would be the best way to begin. From there, you can buy Ethereum, Bitcoin, Bitcoin Cash, or Litecoin.
That’s how most people begin. If you do want to go into altcoins, you would need to sign up for other exchanges; the most popular ones for altcoins would be Bittrex, Binance, and Poloniex (although I think they might’ve all shut down new user sign-ups due to tremendous traffic, maybe they’ve reactivated it).
After signing up for the other exchanges, you would need to fill up those accounts by transferring coins from GDAX to those exchange wallets. One thing I recommend is to NOT transfer Bitcoin because of the high transaction fees and terrible wait time; rather, I’d recommend Ethereum or Litecoin but more so Ethereum because lots of the altcoin exchanges allow you to buy other altcoins with Ethereum or Bitcoin, but if you transfer Litecoin then you’ll have to buy Ethereum or Bitcoin on the new exchange (an extra transaction step, which means an extra transaction fee that needs to be paid) before being able to trade.