You what is transformer and how it works

A transformer is a device consisting of two closely coupled coils (called primary and secondary).
An ac voltage applied to the primary appears across the secondary, with a voltage multipilication propotional to the turns ratio of the transformer and a current multiplication inversely propotional to the turns ratio.
Transformers are quite efficient (output power is very nearly equal to input power);thus, a step-up transformer gives higher voltage at lower current.
Transformers serve two important  functions in electronic instruments:They change the ac line voltage to  a useful (usually lower) value that can be used by the circuit, and they "isolate" the electronic device from actual connection to the power line , because  the windings of a transformer  are electrically insulated  from each  other.