The principle of a transformer is quite simple, to adjust voltage to an acceptable level, depending on the electrical requirements. Transformers operate using a ferromagnetic iron core. There is a primary coil, around which electrical wire is wound around. There is also a similar secondary coil, which has electrical wire wound around it as well. The incoming voltage is either increased or decreased by manipulating the number of loops of electrical wire around the primary and secondary coils.
If one wants to increase the voltage, say double what the voltage is coming into the primary coil, one should double the nuber of coils on the secondary coil. This will cause the induced electromagnetic voltage to be double that of the primary coil.
Consequently, if one wants to do the opposite, to decrease the voltage, one has but to do the reverse. Half the number of loops of electical wire wound around the secondary coil will effectively cut the incoming voltage by half.