This is something every citizen must understand. We’re not taught this in schools. Most of the teachers I had in school believed the Constitution was a ‘living’ document. That is to say, the meaning of the Constitution changes over time. That couldn’t be more wrong. The Constitution is a rigid document. The ONLY way to change its meanings is via the amendment process.
The Supreme Court of the United States spends much, if not most, of its time on a task which is not delegated to the Supreme Court by the Constitution. That task is: Hearing cases wherein the constitutionality of a law or regulation is challenged. The Supreme Court’s nine Justices attempt to sort out what is, and what is not constitutional. This process is known as Judicial Review. But the states, in drafting the Constitution, did not delegate such a power to the Supreme Court, or to any branch of the government.
Since the constitution does not give this power to the court, you might wonder how it came to be that the court assumed this responsibility. The answer is that the court just started doing it and no one has put a stop to it. This assumption of power took place first in 1794 when the Supreme Court declared an act of congress to be unconstitutional, but went largely unnoticed until the landmark case of Marbury v Madison in 1803. Marbury is significant less for the issue that it settled (between Marbury and Madison) than for the fact that Chief Justice John Marshall used Marbury to provide a rationale for judicial review. Since then, the idea that the Supreme Court should be the arbiter of constitutionality issues has become so ingrained that most people incorrectly believe that the Constitution granted this power.
More on this topic can be found on the link above.