Basics: Induction

Faraday's law of electromagnetic induction describes a basic law of electromagnetism, which is involved in the working of transformers, inductors, and many forms of electrical generators. "The induced electromotive force or EMF in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit."
 

A changing magnetic field creates a voltage in a wire.
And...
A changing current in a wire creates magnet flux around that wire.

 Traditionally, two different ways of changing the flux through a circuit are recognized. In the case of transformer EMF the idea is to alter the field itself, for example by changing the current originating the field (as in a transformer). In the case of motional EMF, the idea is to move all or part of the circuit through the magnetic field, for example, as in an axial flux wind turbine generator.