As George Welch is quoted saying; "You fill the seats, and we will give you a show to remember."
Green Flag: Beginning of Race; the track is clear.
Yellow Flag: Caution, do not pass another car, track is unsafe.
Red Flag: All cars must stop now, rollover, fire, or road accident, restart
Black Flag: Pull into pits immediately, may mean that driver is disqualified or that car is considered unsafe to continue.
Blue Flag with Diagonal: A faster car is lapping you, pull over and let him pass.
White Flag: One more lap before race is finished.
Checkered Flag: Race is finished.