Thanks for your question Kirah and Kate! Before federation in 1901 Australia did not exist as a nation but was a collection of six British colonies. When the colonies agreed to federate, or unite, to form the Commonwealth of Australia, they needed a constitution, or set of rules, for how the new nation should be run. The Australian Constitution was drafted at a series of conventions, or meetings, attended by representatives from these colonies. Most of these representatives were members of the colonial parliaments; for example, Edmund Barton – who later became Australia’s first Prime Minister – and Henry Parkes both came from the New South Wales Parliament, Andrew Inglis Clarke was a member of the Tasmanian Parliament and Alfred Deakin came from the Victorian Parliament. After the Constitution was drafted, a referendum – a vote of the people – was held in each colony between June 1899 and July 1900 to approve the document.
The Closer Look paper on Federation has more information about the drafting of the Constitution and the people involved in this process. If you are interested in the discussions which took place during the conventions, check the Records of the Australasian Federal Conventions of the 1890s.