The Supreme Court hears only one or two original jurisdiction cases per term -- disputes where it acts as the first and only court, like fights between states over water rights or borders. The vast majority of its roughly 60-80 annual decisions come through appellate jurisdiction, where the justices review rulings from lower courts after someone files a petition for certiorari.
The distinction matters because it determines who gets access to the nation's highest court and when. Only disputes between states trigger the Court's exclusive original jurisdiction -- no lower court can hear those cases at all. Mississippi v. Tennessee, a groundwater rights battle decided in 2021, went straight to the Supreme Court because no other court had authority. Everything else -- from gun rights challenges to election disputes -- must work its way up through federal or state courts first, a process that can take years. Article III, Section 2 of the Constitution draws this line, and Congress can adjust the appellate side through the Exceptions Clause but cannot touch original jurisdiction.