Thank you for your question. There are many ways that individuals can get involved in the law-making process. You can contact your local representative in the level of government responsible for a particular law. At the federal level, that means contacting the member who represents your electorate, or one of the senators for your state. You can find contact details for all senators and members here.
If a citizen believes that a federal law is unconstitutional or has not been validly made, they may challenge it in the High Court of Australia.