Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end.
Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves – electromagnetic waves.
Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows). The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.
James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.