The Grinch stole Christmas by sneaking into Whoville on Christmas Eve and taking away all the presents and decorations. He tried to ruin Christmas by taking away all the joy and happiness that Christmas brings. But in the end, the Grinch realized that Christmas isn't about the material gifts, but rather about the love and kindness that it brings. So he gave back the presents and decorations he had stolen, and everyone in Whoville had a happy Christmas after all.