If you have worked for your employer at least 40 hours in the 5 weeks before the public holiday and the public holiday falls on a day you normally work you are entitled to a day's pay for the public holiday. If you are required to work that day you are entitled to an additional day's pay.
If you do not normally work on that particular day you should receive one-fifth of your weekly pay. Even if you may never be rostered to work on a public holiday you are entitled to one-fifth of your weekly pay as compensation for the public holiday.
In all of the above situations your employer may choose to give you paid time off instead of pay for the public holiday.