What does the judicial branch do?

In the United States, the government can be organized into three Branches- the Executive, the Legislative, and the Judicial. The Judicial Branch has the power and responsibility for interpreting and applying the law, as well as making sure that the laws brought before them are constitutional. The highest authority in the Judicial Branch is the Supreme Court, made up of eight Justices and one Chief Justice. When the Supreme Court makes a ruling in interpreting the law, all inferior courts must act based on their ruling. A person who is unhappy with the ruling of their case at a common or state court may also appeal to the next superior court and ultimately the Supreme Court, in the effort of proving the unconstitutionality of the first ruling. 

On a day to day basis, the judicial branch interprets the law in hearing and deciding on cases. In the broader spectrum, their interpretation of the law creates and recreates the environment of legality and constitutionality in the United States.