If you intend to work during your time in Australia, you will need to obtain a Tax File Number (TFN). If you commence working prior to getting your Tax File Number, you will have 28 days to provide it to your employer.
You can apply for a TFN in person at an Australian Taxation Office (ATO) or online at: www.ato.gov.au/forms/tfn---application-for-individuals
You will need to complete an obligatory tax return when your Working Holiday finishes or when you stop working. You may be eligible for a tax refund. Visit the ATO website for information on how and when to lodge your tax return.
Ask your employer for a payment summary, showing your total income and the amount of tax withheld, so that you are able to lodge your tax return.