Article III of the Constitution established the judicial branch of government with the creation of the Supreme Court. This court is the highest court in the country and vested with the judicial powers of the government. There are lower Federal courts but they were not created by the Constitution. Rather, Congress deemed them necessary and established them using power granted from the Constitution.
Courts decide arguments about the meaning of laws, how they are applied, and whether they violate the Constitution. The latter power is known as judicial review and it is this process that the judiciary uses to provide checks and balances on the legislative and executive branches. Judicial review is not an explicit power given to the courts but it is an implied power. In a landmark Supreme Court decision, Marbury v. Madison (1803), the courts' power of judicial review was clearly articulated.