A myth is a traditional story without an author that is usually intended to:
teach a lesson
explain one of the many mysteries of life
explain a phenomenon of nature
describe the customs, institutions, or religious rites of a people
In ancient times, something like a clap of thunder must've caused quite a fright. They didn't understand the inner workings of meteorology. Imagine the panic a hurricane or earthquake would've incited.
In order to understand these phenomena and, perhaps, bring comfort to people, myths were created as explanations for the many mysteries of life. Even our ancestors contemplated the creation of earth, natural disasters, flaws in humanity, death, and love.
The word myth is derived from the Greek word mythos, which means "story." Myths usually came about during a time when science, philosophy, and technology were not very precise.
Myths exist in every culture and country. Most cultures have their own creation myth. The majority of myths, regardless of their premise, tend to involve the exploits of gods or heroes who possess god-like qualities.
You'll find that many myths are set in a timeless place and involve a plethora of symbols that have multiple meanings. This is what makes myths such an interesting study: decoding their symbols.