"Why do the Nationals and Liberals work together while the other parties (Labor, Greens, etc) are by themselves?"

In the Australian Parliament, political parties can choose to work together to achieve their aims, create a bigger group and gain more power. This is called a coalition.

The Liberal Party of Australia and the Nationals have formed the longest-running coalition in the Parliament. This is sometimes called the Coalition.

Members of the Coalition (Liberal Party and Nationals members) sit next to each other in the House of Representatives and the Senate. They generally vote the same way, although they may have different ideas on particular bills—proposed laws. Each party holds separate party meetings and elects the leaders of their party.

The Political parties fact sheet has more information about coalitions.

diagram to help explain Why do the Nationals and Liberals work together while the other parties (Labor, Greens, etc) are by themselves?