What is a myth? How did the idea of him change?

Initially, the myths arose on the territory of modern Greece, Egypt and the Scandinavian countries several thousand years before our era.
At their core, myths meant a brief narration of people about the history of mankind, religion, ancient Gods and the very essence of existence.
In ancient times, myths were one of the main historical sources that could not be confirmed or refuted, therefore people considered them to be historical information.
At the moment, myths are considered as the source of a literary or artistic direction.