A republic is a country where power is completely in the hands of the people, rather than sharing that power with a Queen or King like we currently do.
The Queen of England holds the top job as Australia’s head of state. She appoints the Governor-General as her representative to act on her behalf. Her representative must approve every law made by our Parliament, every election and the appointment of every government. Becoming a republic means Australians will do all of this for ourselves without asking the Queen of England or her representative for approval.