The American government is split into three branches. The legislative, the executive, and the judicial. The legislative makes the laws. Executive executes the laws. The judicial branch can repeal the laws or hear cases relating to law. The nine supreme Court justices are the judicial branch and are meant to decide if laws are invalid based on past history and intent. For example striking down slavery or Jim Crow laws. They sometimes stretch the definition to make it work which can be scheduled. For instance, roe versus Wade legalized abortion through a weird interpretation of the right to privacy. There was no actual law that allowed abortion. The supreme Court just enshrined it through their interpretation of previous laws. It’s a simple majority system so as long as 5 vote for a decision, it becomes the decision of the court
The judges are picked by the executive but confirmed by the legislative.