There is no completely satisfactory definition of "myth." To help define myth, people often compare myth with "science" and "religion." Usually, this comparison is unfavorable and myth is relegated to the area of lies.
You probably don't need to know Greek and Roman mythology. I mean, it's not very likely that you'll be in a life or death situation where you'll have to veer your spaceship away from the Titan and King of the Gods (Jupiter) planets and back towards the Love (Venus), War (Mars), and Messenger (Mercury) deities in order to find your way back to Earth. Nor will it make very much difference if you fail to recognize the mythological figures behind the name of your car (Saturn or Mercury). However, as you can see from the preceding sentences, Greco-Roman mythology is pervasive in Western culture.
In common parlance, the stories of the Greek and Roman deities and heroes are indiscriminately referred to as myths and legends. If we wish to be more careful, however, we can differentiate between the two types of story, and between them and folktales and fairy tales, although a story may shift between these different categories, or may contain elements from each of them.
In the Judaeo-Christian religions, the Bible plays a prominent role. Homer's Iliad
play a fundamental role in the mythology of ancient Greece and Rome.
Introduction: The Gods and Goddesses of Greek Mythology and More
Life Begins: Creation of Humans in Greek Mythology
Myth and Legend and Religion
Greek Myths and Legends