At every official Konami Yu-Gi-Oh! Trading Card Game there sits a Head Judge. At low-level tournaments, such as locals, you can expect to only have a Head Judge present. But at higher level tournaments, such as Regionals, there will be many Judges present. In this case the Head Judge will likely remain with the Tournament Organizer to make sure the tournament is running smoothly until he is called by another Judge to give a final ruling.
Meanwhile, the many Judges present will walk around their assigned areas. Their job is to watch the gameplay involved in their area and make sure no one is cheating. In addition, they also have the authority to give rulings as needed. When a player needs a ruling to be given, they raise their hand and call the word "Judge." Then the assigned Judge can come over to view the situation at hand and make a ruling based on what they know. Most often, a Judge will have the right answer, but if a player feels they are wrong or would like confirmation, they can appeal the ruling to the Head Judge. Once a Head Judge's ruling has been given, the player must accept it and continue play following his instructions.