Refrigerant is like a sponge. Squeeze it, and heat comes out of it. Let it expand, and it will soak up heat. Squeeze it outside, and the heat will disperse into the outdoor air. Bring it back into the house and let it expand, and it will soak up more heat. This squeezing and releasing takes place between the otdoor "compressor" and the indoor "evaporator" in the standard household air-conditioning system. Cooling system, to be more exact.
In the midst of this squeezing and releasing, the refrigerant changes from a liquid to a gas. Two copper pipes connect the outdoor compressor, or squeezer, to the indoor evaporator, or releaser. One pipe brings in the compressed refrigerant in its liquid form to the evaporator ,where it is slowly released and allowed to expand. When it expands, the liquid changes back to a vapor, and in doing so, absorbs large amounts of heat from the surrounding air. By turning the fan on, we move this "heatless" air away from the evaporator and supply it with new hot air to soak in. This "heatless" or cool air is also being blown to each room through the supply outlets, while warmer air is being sucked back through the return ducts to bathe the evaporator.
Meanwhile, the expanded refrigerant gas , with its new warmth, is being sucked out of the evaporator into the compressor through the second pipe. This pipe is larger than the one supplying liquid to the evaporator, because the refrigerant has expanded and needs more room. The compressor then squeezes this refrigerant vapor and pumps it through a large system of tubes and fins called the condensor. The condensor also has a fan, the outdoor fan, which drags outdoor air over the refrigerant. The outside air is hot, but still cool enough to "chill" the refrigerant and help it return to the liquid state. So, inside the house is a puddle of heat. We stick the refrigerant sponge into this puddle. It soaks up a load of heat. We bring it outside and sqyeeze it out. Voila! The refrigerator in your kitchen performs this cycle entirely inside. It uses the refrigerant to soak up heat inside the fridge, and releases it out the back in that network hot fins and tubing.