Pure warm air is heated by the temperature of the water tank and does not start the compressor. So no need to waste oil. That's why there is no warm air when the car is cold in winter, and it only comes after driving for a while before the water temperature comes up.
AUTO means automatic. If the air conditioner is placed on automatic, the compressor may start, which may consume fuel. The cold air in summer is cooled by a compressor, which consumes oil.
ECNO is an economic mode. Generally, cars have this choice in gears, and there are corresponding normal modes and sports modes. Some cars have air conditioning.