In the United States, the three branches of Government are the Executive, Judaical, and Legislative.
The head of the Executive is the President, the Job of the Executive branch is to provide for the common defense, and execute the orders and laws of the United States.
The head of the Judaical branch is the Chief Justice of the Supreme Court. The Judaical branch judges civil court disputes, host trials by jury, and can Judge any law past by the other two branches to view if it is Constitutional or unconstitutional.
To learn more, read the Constitution. It is all in there in exact detail.