Online bookmakers have different terms and conditions regarding Bonus bets so check these out carefully. Normally residents of NSW, Vic, WA and SA aren't eligible for any bonus bets, free bets or first deposit matched bets or offers.
All the bonus offers vary but typically you will be required to deposit and bet a certain amount before receiving funds to your account which you can then bet with. Some bookies will require you to bet through or turnover a certain amount, sometimes at or above certain odds before you can withdraw any bonus and even sometimes before you can withdraw your original deposit. So please do check the terms and conditions of each bookie.