Hades is taking Persephone to the under world, by opening up the ground and kid napping her on his chariot. Then taking Persephone to the underworld.
Demeter is running around the fields and woods looking for where Persephone went. while she's looking for Persephone, the trees are loosing leaves, the fields are barren cold on earth
Persephone is in the underworld on a throne. And she's miserable there. There's no flowers or fruit except for one lonely Pomegranate tree.
Demeter went to Olympus and demanded Zeus to tell Hades to bring Persephone back to her. She said if he didn't she wouldn't lt and crops or plants grow on earth and let it shrivel up. so then Zeus ordered Hades to bring Persephone back to Demeter.
In the underworld Persephone ate pomegranate seeds with out realizing, then Hermes came to bring Persephone back to earth. when she left the underworld Hades realize that she ate six pomegranate seeds. That means she ahs to stay there. Then when Persephone got back to earth and saw Demeter her mom again she had tears of joy and made the earth blossom again and the snow melted but then Persephone told her that she had to stay with Hades. However Zeus decided that because Persephone ate six seeds she will stay with Hades for six months and stay with Demeter for the other six months. so while Persephone was with Hades Demeter would make it be fall and then winter on earth. Then when Persephone returned Demeter would make it spring then summer again.
So now Persephone is with Hades for half of the year. And that's when Demeter makes it fall then winter on earth. Then when Persephone is back with Demeter on earth, Demeter make it spring then summer.