www.business.gov.au has a guide. If you Google 'starting a business in Australia' look for government sites. The ATO has info too.
Hi OP - that's awesome!! Have a look through the posts in our small business hub, as there'll be loads of info you'll find useful. https://www.stayathomemum.com.au/small-business-hub/
We also have a Facebook group that you are welcome to join to ask questions and get more info https://www.facebook.com/groups/TenaciousBusinessDevelopment/