You need to ensure you meet the current COVID-19 travel regulations and advisories for your departure point, destination, and any transit points prior to booking. This includes border declarations, testing and quarantine requirements.
If you need to book a pre-departure COVID-19 PCR test, you can do that here.
Australia's border are currently closed except for travellers to and from New Zealand.
A two-way quarantine free bubble exists between Australia and New Zealand, however this arrangement may be paused in the event of a COVID-19 outbreak in either country. For border declaration, testing and quarantine requirements, visit the Smart Traveller website here.
Other international travel
All other international travel is currently banned for Australian citizens and permanent residents without and exemption. Temporary visa holders and visitors do not require an exemption to leave Australia, but will need one to return. All passengers arriving into Australia are required to pay for their own government-directed quarantine, except for those arriving from New Zealand who are not required to quarantine.