Hades kidnapped Persephone, daughter of Demeter (goddess of the harvest), by tricking her into picking a flower.
He made her his wife and she was terrified at first but later she sort of liked the way she and Hades could boss people around.
Demeter begged for Zeus to make Hades let her daughter go. Zeus agreed but only is Persephone hadn't eaten anything from the underworld.
But when Hermes went to go get Persephone it turned out that she had eaten six pomegranate seeds.
The Gods agreed that because she only at six seeds that she would only have to stay six months out of the year.
So that is why we have seasons, because when Persephone goes to live with her mother, Demeter is happy so we have nice weather and it's summer. But when Persephone goes to the underworld to live with Hades, Demeter is sad, so we have cold weather and winter.