The simplest of them all. It means the session has officially ended and is waved until all cars have crossed the line.
The green flag means the track is clear and there are no issues ahead. It is used in practice sessions, qualifying and the race.
The bright-yellow flag means there is a hazard up ahead and for drivers to approach with caution. It comes in two forms: a single-waved yellow and double-waved yellow.
In both cases, a driver must slow down, avoid overtaking and must be prepared to avoid a hazard up ahead. In a double-waved yellow, they must slow down considerably, as it is often used when marshals are on track. In practice of qualifying, drivers must not attempt to set a competitive lap time.
This flag is used to stop a practice session, qualifying session or race due to a serious accident or extreme weather. Officials make the call to bring out the red flag and they are then waved at the start line and marshals posts. Drivers must reduce their speeds and proceed back to the pit lane. In practice and qualifying they go to their garages and in the race, they line up at the pit lane exit.
Blue flags inform a driver that a faster car is behind them and looking to overtake. In the race, it means a driver is behind lapped and they must allow the faster car past as soon as they can. In practice and qualifying it means a faster car is approaching them, or they have exited the pits and a quicker car is behind.