Neat coin, Sara. It is made of aluminum bronze. Coins like this, found in circulation and made of non-precious metal, are worth face value. According to xe.com, one Australian dollar is worth about 80 US cents (at the time of this writing, better look it up), so a 2 dollar Australian coin is worth about $1.60. If you tried to cash in your 2 dollar coin for American money, the currency broker would charge a fee, so $1.60 is a maximum value.
If exchange rates change, the $1.60 value changes also.
Collectors are willing to spend more than face value for nice-looking specimens of modern coins. If you go on eBay, you will find that uncirculated coins like this sell for a few US dollars, so that is how much they are worth if you are willing to put in the time, effort, and cost of making eBay sales.