The most important element in a refrigerator is a fluid known as a “refrigerant”.  Fundamentally, the refrigerant will form a circuit that basically allows heat to be extracted from a cold region (such as the inside of the refrigerator), to a warmer area (such as the surrounding area, i.e. the kitchen).

The cycle of this heat engine starts off with the compressor constricting the refrigerant vapor, which increases the pressure and then forces it into the coils on the backside of the refrigerator. This then causes the hot gas in the coils to become a liquid. The liquid refrigerant then cools down as it flows through the coils on the inside of the refrigerator. This leads to the refrigerant absorbing the heat inside of the refrigerator causing the inside of the refrigerator to become cool. During the last portion of the cycle, the refrigerant evaporates into a gas, which then flows back to the compressor to restart the cycle. Essentially, in order to refrigerate the substance, energy must be accumulated from a cold region and exhausted in a warmer region.