The coolant that keeps the engine from overheating is below the minimum level. A leak is the most common cause.
Can I keep driving?
Don’t drive far. Low coolant can lead to overheating, which can wreck an engine. Top it up and watch the temperature gauge.
What to do
Switch the engine off and let it cool completely. Never open the radiator or reservoir cap on a hot engine: it can spray scalding liquid.
Look at the see-through coolant reservoir. The level should sit between the MIN and MAX lines.
Top up with the coolant type in your owner’s manual. Plain water is only a short-term emergency fix.
If the level drops again, there is a leak. Get it checked before long drives.
If the temperature gauge climbs into the red, pull over safely and switch off the engine.
General guidance, not a diagnosis. Warning lights vary between cars, so check your owner's manual too. If you're ever unsure or the car feels wrong, stop and call for help.