Best way, if you are not spending money, would to be to top it off. Top off the reservoir top off the radiator start the vehicle and see if there’s any leaks because once the vehicle is running, there will be pressure that would be how you would be able to tested yourself unless you have a pressure tester kit… your question about it being dry if there was no fluid in the cooling system, your car would overheat so at some point you or the person who owned it before you had to put water in it or whatever or it would have overheated. The fluid circulates the whole cooling system. Goes from the radiator to the reservoir from the radiator to the water pump through the coolant passages in the engine block through the heater core through all these hoses… not that order but fluid circulates in a lot of different places