A transformer is a device made from core of soft iron with two or more insulated coils of wire, which are not connected. The main function of a transformer is to change the voltage or alternating potential difference from one state to another. The voltage is increased or decreased via a process that involves electromagnetic induction. The name of the device is taken from its main function, which is to transform voltage.
How does a transformer work?
  A transformer is a voltage ratio device  primarily because the amount of transformation is dependent on the turn ratio  of the two sets of coil. The primary winding or input coil magnetizes the core  when an alternating voltage is applied. The first coil affects the secondary winding  or output coil. When the core is magnetized, voltage is induced in the  secondary coil by the changing magnetic field. The ratio is 2:1 if the primary  coil has 100 turns and the secondary coil has 50 turns.
What is a step-up transformer?
  A step-up transformer is a device that  features more turns on the secondary winding than the primary. As a result, the  induced voltage is greater than the alternating voltage applied to the primary.  In territories that offer consumers a 110-volt electrical supply, a step-up  transformer is necessary to power electronics hardware that runs on 220 volts.
What is a step-down transformer?
  Meanwhile, a step-down transformer  contains more turns on the primary coil than the secondary. As such, the  voltage on the secondary winding is lower than the voltage applied on the  primary.