Final answer:
The U.S. Supreme Court has original jurisdiction in cases involving Ambassadors, public Ministers and Consuls, and in cases where a state is a party. These cases represent a small fraction of the Court's workload, as it primarily functions as an appellate court for other cases.
Step-by-step explanation:
The U.S. Supreme Court has original jurisdiction in certain types of cases as delineated by the Constitution. This special jurisdiction allows the Supreme Court to hear cases first, before any other court. The cases under the Supreme Court's original jurisdiction involve those affecting Ambassadors, public Ministers, and Consuls, and those in which a state is a party.
These cases are heard by the Supreme Court directly, not on appeal from lower courts. The Supreme Court's original jurisdiction is fairly unique as the number of these cases is quite low; they constitute less than one percent of the Court's docket. For all cases not under its original jurisdiction, the Supreme Court generally functions as an appellate court.
This means that the Court reviews decisions from lower courts that are brought to it on appeal and has the power to affirm, reverse, or remand these cases based on its interpretation of the law and the Constitution. The decision to take on these appellate cases falls to the discretion of the Supreme Court; of the tens of thousands of cases petitioned each year, only a fraction are selected for review.