While not technically a form, you will need an agreement that sets out the terms of employment for your new employee. Agreements must meet the minimum requirements of the Fair Work act. You can find more information on the Fair Work website.
If you need help creating an employment agreement, business.gov.au has an employment contract tool. According to their website you can “Build your own employment contract, for an employee under Australia’s Fair Work System, that is tailored to your business needs”.
If you need further advice or your new hire falls into the category that the employment contract tool is not suitable for, consider using the services of an employment lawyer.