Transformers are an application of mutual inducatance, caused by inductors. Transformers transfer power between two inductors that share a mutual core. Two sets of windings (giving winding is primary, pulling winding is secondary) are used and rated in the given direction, however it works both ways.
By using different amounts of windings on each side we can step up or down voltage and current. This is because the same amount of energy is on both sides, however if there are fewer turns then the energy is more concentrated, leading to a step up transformer.
The relationship between input and output voltages are based upon the primary winding Np to the number of turns on the secondary winding Ns. The relationship with their voltages E is shown below
Es / Ep = Ns / Np
Es = Ep * Ns / Np
What is the voltage across a 500 turn secondary if 120V is across a 2250 turn primary?
120V * 500 / 2250