What does the radiator in a car do?

Answer 1

As coolant cycles through the engine, it absorbs heat from the engine, after which, it continues through the cooling system back to the radiator. As the coolant passes through the radiator, the heat is exchanged to the ambient air by way of airflow through the radiator fins (this is why it's important not to bend the radiator fins).

Answer 2

The radiator serves as a heat exchanger. The coolant absorbs heat from the engine as it passes through the cooling system. It loses this heat in the radiator, as heat from the coolant is transferred to the air which flows through the radiator.