Firstly, you can choose whether to pay HECS or FEES.
If you choose HECS, it is the normal UAI cut-off and you will gain a debt which is garnished from your salary once you reach a certain amount.
If you choose FEES, the cut-off will be up to 5 points lower than the HECS cut-off, but you will have to pay upfront and a much larger fee.
Then, if you decide you want to take out a loan to pay for the FEE-paying option, the government will pay the upfront FEE payment for you now and you will have a debt which is garnished from your salary once you reach a certain amount. The maximum amount the government will pay (ie. the maximum loan) is $50,000. Note that borrowing to pay for FEEs will leave you with a much higher debt than HECS. There is also a 20% fee on the loan as well, additional to the amount you borrow.