The Flags
 
Green - GO, All Clear to Race
Red - Stop Racing

Yellow (Stationary) - Take care as a driver is still in a stationary car, but continue to Race
Yellow (Waved) - Race Suspension, All Cars must remain in single file and slow to 15mph, or in exceptional circumstances stop. No Overtaking is permitted
Blue - Driver must hold their line as faster cars are trying to overtake
Chequered Flag - Race Winner
Black - Driver disqualified for an infringement - driver must leave the track immediately
  White Flag with Red Cross - Technical Disqualification Flag.This is used to signal to a driver that they have a problem with their car and must immediately retire to the infield
Black Cross - Driver under surveillance for a rules infringement, may be penalised after race conclusion
White flag with Blue Centre - Drivers should exercise caution as oil or other debris may be on the track
Blue & White Striped flag - Give up your position - you have failed to give other drivers a racing line and a fair chance to overtake. Shown when overtaking driver is making continued efforts to pass and is being badly baulked. i.e Blue Flag being ignored