Final answer:
Appellate courts review cases from lower courts to check for legal errors and ensure a consistent application of the law. The U.S. Supreme Court largely functions as an appellate court, aside from a few cases of original jurisdiction.
Step-by-step explanation:
Appellate courts hear cases on appeal from lower courts, typically after a trial or a decision has been made at the initial court level. These courts do not conduct a new trial but rather review the proceedings from the lower court to determine if there were any legal errors that affected the decision. If such errors are found, the appellate court may reverse or modify the lower court's decision. The United States Supreme Court, for example, exercises largely appellate jurisdiction and is the highest appellate court in the federal system, hearing cases from the federal circuit courts of appeals and state supreme courts when federal issues are involved.