How did the element of gold form in the universe?

Gold, and all the other elements heavier than carbon, were formed by nuclear fusion in the centers of stars during supernova explosions. When a very massive star explodes in a supernova, the core of the star is crushed into a black hole, and the rest of the star is blown away out into space.

Billions of years later, the dust condenses in a new planetary nebula and becomes part of a planet.