You will know if your car overheats if the temperature gauge reaches the top portion of your temperature gauge. During normal operation the needle on the temperature gauge should (after approximately ten minutes of driving) stay around the middle of the gauge a little lower during cold weather operation a little higher in warm weather or when under engine load. The cooling system is cooled by air flowing through the radiator when driving at speed or is cooled by an electrical or mechanical fan in stop and go driving.
The cooling system is a "sealed system". It should not require frequent topping up. If your car severely over heats the gauge will stay for a prolonged period at the top oft he gauge, coolant may be "pushed" out of the radiator and coolant expansion tank and hissing and gurgling may be heard from the engine compartment perhaps accompanied by steam.