Without coolant the engine would overheat and seize within minutes.
With just water in the system you would risk the water freezing during cold weather and water alone will corrode the the engine and radiator.
A 50/50 mix of water and anti-freeze will prevent freezing (down to a reasonable level) and prevent corrosion of engine parts.
Hi when water freezes it expands so it does damage like crack the cylinder block and make holes on radiators both in the car heater system and the cooling radiator on the front of the car.
so we mix water with glycol a chemical which does not freeze at 0 zero degrees C. so the amount of glycol added will vary. however in places like canada they use nothing but glycol or antifreeze. because the temperatures can go down to minus 40 degrees C. so mixing water with it is not a good idea.
so sadly Andrel has got it all wrong. it is mixed with water in more moderate climates like the the `United kingdom where we only expect a drop in the winter months to a maximum of minus 12 degrees `C.
We use coolant mixed with water 50/50 so that the engine will run at the perfect temperature. Use too much coolant and the fluid will be too thick and the engine will overheat, use too little and it wont cool effectively.
