The visa information site of the Australian Department of Home Affairs is the authoritative source of information about visa requirements for visitors to Australia, including the application process, and you should check that site for the most comprehensive and up-to-date information.
In general, if you do not have a current Australian passport, you will require a visa of some kind to attend the conference. Please use the Home Affair Visa Finder to determine which class of visa you require. The Home Affairs travel site also contains additional information about travelling to Australia.
Support Letters for Visa applications
Some classes of visa may require support letters from the conference organizers. If you require such a letter, please fill in this form.