Just like the condenser, the evaporator contains many coils for the refrigerant to travel through which increases the surface area for the transfer of heat energy. This time, the refrigerant is low in pressure and the fan is blowing in air from the room.
The high pressure, hot room air has its heat energy transferred into the refrigerant and the newly cooled air is ejected back into the room. The refrigerant, now containing heat absorbed from your indoor air, goes back into a vaporous state and begins the cycle again, travelling through the compressor towards the condenser to exhaust the heat it has absorbed.
Even air form the inside of your home will contain dust, debris and dander which can build up on the coils reducing the overall performance of the cooling system and shortening its lifespan. Make sure to clean the coils now and again.