The Supreme Court of the United States constitutes one of the Three branches of our government. It is powerful, some say the most powerful of the branches, dynamic in its evolution, and political as has been witnessed many time through its history. The total number of justices sitting on the Court is nine (since 1869). These positions are appointed. For more about the structure of the Federal Courts, follow these links.
The Creation of the Supreme Court
Original and Complete text from the Avalon Project