Basically a transformer consists of two coils of wire that are insulated from each other. The coils are wrapped around the same laminated iron core. The coil which power is supplied is called the primary. The coil from which the power is delivered is the secondary.
Alternating current flowing in the primary induces an alternating flux in the core. The continual building and collapsing of this flux induces a voltage in the secondary. Thus a transformer transfers electric energy by magnetic induction. There is no change in the amount of electric power except fot the heat losses.
Also the transformer is a discovery of Faraday.