The Supreme Court only hears cases that are important to the nation as a whole or when there's disagreement over federal or constitutional laws, notes the Federal Judicial Center. For example, the Supreme Court could hear a case when there's a question about an amendment of the Constitution being violated. Its purpose is law clarification rather than overriding decisions that other judges have made.
The Supreme Court is very picky about the cases it actually reviews, with about 80 of 8,000 cases chosen a year, notes the Federal Judicial Center. In addition to examining whether laws are constitutional, the Supreme Court also looks at law interpretation to find issues with laws that Congress passes.