Racing uses a lot of flags to signal the drivers to keep them aware of the race conditions or of danger.
The green flag is start, the blue (with diagonal yellow stripes) is to allow a car to lap or overtake another (double blue flags for second warning), black is to head back to the pits, yellow shows danger and passing is not permitted, red is all stop, white flag (with red cross) is an emergency vehicle on the track, white flag is starting of the last lap, surface flag (yellow with red stripes) is track condition compromised due to contaminants like oil, fluids, etc and the checkered flag is the end of the race.
