A child born in Australia is a citizen when a parent is a citizen or permanent resident, or when the child is ordinarily resident in Australia for the first ten years of life.
Sources: Australian Citizenship Act 2007
The general residence requirement is four years on a valid visa, including the final 12 months as a permanent resident or eligible Special Category Visa holder.
Sources: Australian Home Affairs — Citizenship residence calculator · Australian Citizenship Act 2007
A person born outside Australia may apply by descent when a parent was an Australian citizen at the time of birth.
Sources: Australian Home Affairs — Citizenship by descent · Australian Citizenship Act 2007