The microwave oven cooks by using radio waves to heat certain types of molecules in food (water, fats, bone). The microwave oven cooks food from the inside (unless the food is surrounded by the water or fats.)
An electronic appliance that heats food using electromagnetic radiation in the microwave spectrum, a microwave uses the process known as dielectric heating which causes polarized molecules in the food to rotate and build up thermal energy which in turn results in food heating efficiently and quickly. The microwave oven is primarily used for reheating pre-cooked food and for heating slow-cooking items such as butter chocolate and fats. However, microwave ovens cannot be used in professional cooking since flavours produced by frying, baking or browning cannot be achieved through a microwave oven.
Microwaves are available in different sizes such as portable or desktop, compact, medium capacity, large capacity and built-in.
In conclusion, one can say that the primary task of a microwave is heating food.