A variety of flags are used at performance driving schools. Some are obvious; others are less so. The track marshals use flags to communicate with the driver, to communicate if something is wrong with the car, or if hazards ahead on the track, or if the driver is being penalized.

N.B. The meanings are different in some cases than what is used in racing... For example, typically in racing, a white flag means "last lap."

red steady or waving	Stop! Indicates there is a very serious incident that requires all cars to complete stop as safely yet quickly as possible. Do not "hit" your brakes. Pull to the side of the road, stay on the track but well off the "race" line. Do not proceed until directed by a track or event official. Watch your mirrors to ensure no one rear-ends you...
(()) yellow waving	Danger ahead! Slow down, do not pass There is a serious incident that requires drivers proceed very cautiously, possibly quite slowly. Typically, yellow flags are waved at the corner where the incident has occurred or one corner immediately ahead. Look and plan well ahead. Do not stop.
yellow steady	Caution! Do not pass There is an incident, usually off track, that requires some caution from the remaining drivers. Look and plan well ahead. Be prepared to slow; do not stop.
double yellow steady	Full course slow down, do not pass This is an indication of a "full-course yellow." Usually this means there is an incident which is unsafe so passing cannot occur and speed must be reduced. Safety marshals and rescue teams are possibly on or near the track surface. Watch for white flags and slow moving vehicles.
yellow/red, striped steady or pointed	Debris, oil The "surface" flag means there is debris on the track ahead. The debris may be in the form of car parts, stones, or grass. If there is water or oil or coolant on track, the same flag is used. Proceed with some caution and be aware of changes in tire grip. Corner worker may point where debris is.
white steady or waving	Slow vehicle ahead There is a slow moving vehicle on track. This may be a car exiting the pits and coming up to track speed. It might be an ambulance or service vehicle. Look well ahead and check mirrors.
black pointed at you	Infraction, enter pits ASAP! This indicates either something wrong with the car or the driver has committed an infraction (perhaps passing under yellow). Proceed immediately to the pits (do not stop on track) and discuss the matter with a track or event official.
black all corners	Black flag all, return to start/finish! Proceed slowly to the pits or the Start/Finish line or the pits to be re-gridded. Await further instructions as directed by a track or event official.
black with orange circle	Mechanical, enter pits ASAP! The "meatball" flag indicates something is wrong with the driver's car. Proceed immediately to the pits (do not stop on track) and discuss the matter with a track or event official. Be gentle with your vehicle and "feel" for handling problems; be aware of unusual smells.
((())) blue waving frantically or pointed at you	Let car behind pass ASAP! A vehicle that is travelling faster than you wishes to pass. A vigorous point from a corner marshal usually indicates the lead car should let the pass occur immediately. Let the car pass in the next passing zone. Some blue flags have a diagonal yellow strip.
(()) blue waving	Let car behind pass A vehicle behind you is travelling faster than you and gaining. Check your mirrors. Prepare to let the trailing car pass soon.
blue steady or "peeked" at you	Check your mirrors There is a fast car behind but they are still a ways back. Nevertheless, they're coming so get ready to let them pass.
green steady or waving	Go, proceed, passing allowed Proceed at speed. May not necessarily mean the entire track is clear; perhaps only this corner.
(()) white/black, checkered waving	Session over The track session is complete and the track will be closed. Complete one more lap, a "cool down" lap. Proceed slowly and do not use the brakes so to permit the brake components to cool down and to avoid boiling the brake fluid. It is also an opportunity for the driver to cool down...