who formed it?
Australian Government
Australian Defence Force
During the first decades of the 20th century, the Australian Government established the armed services as separate organisations. Each service had an independent chain of command. In 1976, the government made a strategic change and established the ADF to place the services under a single headquarters. 
when did the australian defence force establish? 1976
wiki:13465737
Australian Defence Force [SEP] Introduction
Over time, the degree of integration has increased and tri-service headquarters, logistics, and training institutions have supplanted many single-service establishments. The ADF is technologically sophisticated but relatively small. Although the ADF's 58,206 full-time active-duty personnel and 29,560 active reservists make it the largest military in Oceania, it is smaller than most Asian military forces. Nonetheless, the ADF is supported by a significant budget by worldwide standards and can deploy forces in multiple locations outside Australia.