An air conditioner is a machine that helps make a space, like a room in your home, cooler. It works by moving heat from inside the space to the outside, while blowing cool air inside. It's like a fan, but it also has a special part that changes the air's temperature. When you set your air conditioner to a certain temperature, it uses its special part to cool down the air to that temperature and then it blows the cool air inside the room.