When should the fan in a laptop be turned on. can a lap top overheat?

Its i was wondering what the button for the fan was for on my laptop. i am new to laptops.
Answer
Usually fans inside of laptops are running when the laptop is on. it is possible you could have a low heat laptop and the fans will activate as necessary as the temperature goes up, but they are definitely necessary. a laptop can definitely overheat. the most likely cause is if the holes where the heat is released from are covered for an extended period of time while the laptop is on.