Ancient Greeks used myths about their gods primarily to

A myth is a story about how things came to be. calling a story “a myth” doesn’t mean it’s not true, just that it’s some nation’s interpretation of how everything around us showed up. So myths are primarily an explanation of the origins of the world.

And then the characters in the story took on a life of their own: the gods has good and bad qualities, just like humans, and they desired things, and hated others. Something as ugly and yet as interesting as a spider had to have a good explanation — a beautiful maiden, who had the gift to weave, and made Athena jealous. Or twin births — perhaps one of the children was human, while the other was that of the notorious womaniser Zeus.

And maybe later on (but this is pure seculation on my part, I haven’t studied this area), authorities would use these myths to gain more power and make people obey because of fear (like the Roman emperors, starting with Augustus, who claimed to be gods themselves).

also to explain events in the natural world