What we call electrical current occurs on the particle level among the atoms of a conducting material—in a household circuit, this is the copper wiring. In each atom there are three types of particles: neutrons, protons (which carry a positive electromagnetic charge) and electrons (which carry a negative charge). The important particle here is the electron, since it has the unique characteristic of being able to separate from its atom and move to an adjacent atom. This flow of electrons is what creates electrical current—the jump of negatively-charged electrons from atom to atom.
How Generators Work
What sends the electrons into motion? The physics are complicated, but in essence, electrical flow in circuit wires is made possible by a utility generator (a turbine powered by wind, water, an atomic reactor, or burning fossil fuels). In 1831, Michael Faraday discovered that electrical charges were created when a material that conducts electricity (metal wire) is moved within a magnetic field. This is the principal by which modern generators work: The turbines—whether powered by falling water or steam created by nuclear reactors—rotate huge coils of metal wire inside giant magnets, thereby causing electrical charges to flow.
With this massive electrical field of positive and negative charges established, the electrons in the wires throughout the power grid jump into action and begin to flow in cadence with the electrical field. When you flip a light switch or plug in a lamp or toaster, you are actually tapping into a large utility-wide flow of electrons being pulled and pushed by utility generators that may be hundreds of miles away.
Electrical generators are sometimes likened to water pumps—they do not create the electricity (just like a water pump does not create water), but they make the flow of electrons possible.
Source: The Spruce