The principle of separation of powers refers to the powers of the federal government. It means that power at the central level is separated between the Executive, Judiciary and the Legislative.
The Legislative has the duty to make laws for the country in line with the Constitution and the Executive has to enforce those laws as well as the Constitution. The Judiciary interprets the law to ensure that it is Constitutional.
There are also duties that can only be performed by one branch such as the legislative having control over the declaration of war but the Executive being in charge of the army. These ensure that no one branch can abuse its power.
