It tells slower drivers who are more than a lap down to show courtesy and let the leaders pass. This is the only flag that drivers may choose to ignore. The black flag tells a driver to report to the pits immediately. It can signify that there is a problem with the driver's car, or that the driver has broken some type of rule, or simply that a driver is going too slow. In any case, the driver who receives a black flag must report to the pits.
Red means stop.
When the red flag is waved, everything comes to an immediate halt. Cars must stop regardless of their position on the track and no work may be done on the cars. This flag indicates that the race leader has started the final lap. It is only shown once during the race. This flag is flown when the winner crosses the finish line and the race is completed.