Coolent light has come up on dashboard.what does it mean.

Not that familiar with bmw's to know if you have a separate coolant LEVEL light as well as a temp light. so, if you have both then it is a level sensor tell you your coolant is low. add a mixture of 50/50 antifreeze(you can but this at most any auto store) to you coolant overflow tank. run engine until it is warm and then let it cool off. *** it cools it will draw coolant back into the radiator until it is full.it may take more than once to get it full. when you are full you should have about 1/4 of the overflow filled when the engine is cold. If you do NOT have the second light then it is telling you the engine is starting to overheat, which is for the same reason just more critical. do the same thing but make sure you do not have a busted hose or other leak, and that your engine is not putting out white smoke. if either of these then let me know. otherwise it is probably just evaporated over time.