Stickers are items that are included in many sets. They can be found with the bricks inside the box, on a slip of paper. To place, simply peel them off and put them on the smooth side of LEGO bricks.
Many fans were disappointed to see stickers replace pieces with decals printed on, saying that they are less durable and hard to put perfectly. Some sets do still occasionally have printed parts, though.
Often, stickers peel off on their own, causing the parts to lose value. In many sets, stickers overlap multiple parts, meaning that the parts have to stay together or the stickers are destroyed.