Engine Coolant Warning message on 1993 BMW 740iL

My son just bought this car....the engine coolant warning came on...and I cant find where to put engine coolant...also there is an empty container left of radiator...what is that for? and how do I fill it

Asked by for the 1993 BMW 740iL
The empty container next to the radiator is the coolant bottle. If it is empty, then that means that the coolant went some where. This needs to be looked at. The bottle should not go dry all by itself.
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You must fill the radiator if it is low. the plastic container you see is the for the window washer fluid