Low coolant, missing belt, failed water pump, inoperable fan, warped/cracked head, restricted radiator, etc.
The engine will overheat and the pistons will seize.
It will not cause the engine to overheat. You have another problem.
There is a warning light which flashes when the engine begins to overheat.
Yes, it controls the coolant flow around the engine block, without coolant the engine would overheat.
You are not giving enough information to get a reasonable answer. It's like asking why it won't start. Any, and I mean any, detail would help. Are we talking about the engine cooling system? What are the symptoms that bring you to the conclusion it is overheating? Have you checked the coolant level? What year and size engine? Does it overheat only when stressing the engine, like climbing hills? Does it overheat only in traffic and okay on the highway? Does it overheat when the car is idling? Has the head gasket ever been replaced?
The answer will depend on what engine it is and what it is being required to do.
Evidently the cooling fan is not working.
its purpose is if the engine was to extremely overheat it would blow out saving your block from cracking
Oil is used in the engine for lubrication and for cooling. If the engine did not have oil it would overheat and soon seize from the heat and wear on engine components. This would destroy the engine in a very short period of time.
it is possible for heat from combustion to cause an engine to overheat quickly depending on where the gasket is blown, but i would look for a lack of coolant circulation first. if your coolant is not getting out of the motor and into the radiator it will overheat very quickly.
It will overheat the engine
The overheat of the engine. You could find some information on Wikipedia.