So you're just looking for a temporary stay in the US? Of all the options available, you've probably picked the easiest one, so nice work!
ESTA Visa-Waiver Program
This is the program that the majority of visitors to the US from Australia will be using to get here. To put it simply, you can come to the US without a Visa, for up to three (3) months but you must not work or do anything really to do with work.
I could write all sorts about this, but I instead just recommend you go to the official Government website: https://esta.cbp.dhs.gov/ and do everything they tell you.
Read everything carefully, make sure you follow the rules. If you do stuff up (or lie), you're going to find it very difficult to return to the US later.