To make a Christmas card pop up, you'll need to cut out a piece of cardstock or construction paper in the shape of a Christmas tree, present, or other festive shape. Then, fold the card in half and attach the pop-up piece to the inside with glue or tape. Decorate the card with glitter, stickers, or other festive embellishments. When the recipient opens the card, the pop-up piece will appear, creating a fun and festive surprise.