Hi Brett! Thanks for asking. The principle of 'separation of powers' proposes that the power to govern be divided between different bodies to avoid any one branch having all the power. Power is divided between a law-making body (Parliament), an executive body (Executive) and courts (Judiciary).
The Australian Constitution divides the power to govern Australia between the Australian Parliament (that makes laws for all Australians), the Prime Minister and ministers (who put the law into action), and the High Court of Australia and other federal courts (that make judgements on the law).