Electric Motors are used in everything ranging from vacuums to hybrid cars. Running an electric motor backwards is, conceptually, similar to how an electric generator works. On a high level, an electric generator converts mechanical energy into electricity. It does this through electromagnetism. When an electric conductor, such as a copper wire, is moved through a magnetic field, electric current will flow through the conductor. The magnets apply pressure onto the electrons in the conductor causing them to move, creating a flow of electrons also known as electricity. The number of moving electrons is called the amperage or the current and is measured in amps. The pressure pushing the electrons is called the voltage and is measured in volts. Note, metals are good conductors of electricity because the electrons are free to move in a network of metal atoms.
Below is a video describing this process in reverse for an electric motor.
