Land-based gambling is legal in Australia, it is lobbied for, it brings in money to the treasury and the businesses are obliged to give some back to the needs of the local communities. Up until 2017, online gambling was also legal, but the new Interactive Gaming Amendment Bill restricted access to virtual wagering and forced a lot of businesses to close. Along with the in-country places to bet and win, many international gaming venues also cut Australia access to their lobbies. As you are getting started, you will see many experienced players on forums reminiscing about how much fun they had playing on slots from Microgaming or enjoying live dealer lobbies from Evolution Gaming. All of this was available until 2017.
That being said, Australians are still welcomed in many offshore online gambling brands. They will have certain licensing from jurisdictions of Curacao, Panama, Cyprus, and a few others. They will also have a limited selection of software developers that can legally work with Aussies. There will be no repercussions for the players for registering at such betting venues.