You must have health insurance while in Australia. Health insurance can be provided by obtaining Overseas Student Health Cover (OSHC) which provides medical and hospital insurance.
See: Overseas Student Health Cover – Frequently Asked Questions

You can ask your education provider to organise OSHC for you, or you can select an approved OSHC provider yourself and pay the insurance.
Exceptions: You do not need OSHC if you are:

• a Norwegian student covered by the Norwegian National Insurance Scheme
• a Swedish student covered by the National Board of Student Aid or by Kammarkollegiet
• a Belgian student covered under the Reciprocal Health Care Agreement with Australia.

If you are studying at more than one educational provider and both are arranging OSHC, you will have to ensure that there is no gap between policies. This means that as one policy expires the next commences immediately.

OSHC is available for a period of up to five years. If your course exceeds five years in length, then OSHC providers may issue cover for a longer period.

If you have a child born after your arrival in Australia, and you only have a single OSHC policy you must change that to a family policy. If family members join you after your arrival in Australia they will have to demonstrate that they have an OSHC policy for the duration of their visas.

Proof of insurance: When you lodge your application, you must provide a receipt or other proof of your OSHC payment. The OSHC should commence when you arrive in Australia.