On the Kids Desk and Photo Desk, you’ll find the stickers icon on the left side toolbar. While on the Doodle Desk, the sticker icon is located on the top middle toolbar.  
Tap on the sticker icon to invoke the stickers library. Browse through 100’s of cute stickers spread over 15+ categories. Simply tap on any one of the stickers to make it appear on the canvas/photo. The placed sticker on your canvas will appear with 4 controllers on each of its corners. The first controller can be used to delete or remove the sticker from the canvas. The top right controller can be used to rotate the sticker. The bottom left controller to flip the sticker and the bottom right controller for the resizing purposes of the sticker.