Any one of the referees on the pitch during a match is considered an official. However, many times, the head official will be denounced prior to the match starting. The head official is in charge of all the other referees, and ultimately makes all final decisions on the pitch during a game, including when to award fouls and cards.
The head referee is responsible for enforcing all laws and rules of the game, from timekeeping and calling penalties to ensuring the ball meets proper requirements. The head referee also is in charge of stopping play for an injury and providing a post-game match report. They can also dismiss a manager from the sideline if they see fit, depending on how much the manager is disrupting play.
The head referee follows the run of play up and down the pitch, staying relatively close to the ball. There are linesmen on either side of the pitch, who will signal for play to stop when necessary via assistant's flags. The fourth official is located on the sideline between each team's bench.