Electrons can flow between certain different materials providing a current, as in a common battery.
While reliable and portable, chemical batteries run down quickly. To provide the large amounts of steady power demanded by modern societies, large power plants have been built. Most power plants make electricity with a machine called a generator. Generators use the principle of electro-magnetic induction, which exploits the relation between magnetism and electricity. As they move, the magnets induce an electric current in the wire.