Great question! The Prime Minister is the leader of the party that is in government. The Prime Minister is chosen by their party and can keep their job as long as they are a member of parliament and have the support of the government. Because of this, the Prime Minister will want to work with their party and ensure that what they say has the support of most of the members of the government.
The Prime Minister is also not able to make laws for Australia without the Parliament’s approval. Australia has a separation of powers, whereby as a member of the Executive, the Prime Minister can propose ideas for laws for Australia. The Prime Minister is also a member of parliament who makes the laws for Australia, but in the parliament the Prime Minister is only one of over 200 parliamentarians who debate and vote on ideas for laws.