They're cold. Really cold.
Colder than Fridges.

Freezers work by taking heat from inside the appliance and transferring it out. This is achieved by the repeated evaporation and condensation of a substance called a refrigerant.
The heat required to make the refrigerant evaporate is taken from inside the compartments. Then, when the refrigerant is condensed, it gives out heat, which is released outside the appliance.

Temperature control
Freezers have a thermostat to maintain the proper temperature. These are usually very simple devices. When the freezer reaches the set temperature, the thermostat interrupts the electricity flow to the compressor, which stops cooling.

Part of why a Freezer works is the heat pump somewhere inside. A heat pump is a device that moves heat from one place to another

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i like trains. Sorry, I don't like trains.

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Freezers are not to be mixed up with Narnia. The link below provides details if you believe Narnia is indeed in your freezer.