To find them, open the app, tap the camera icon to the right of the search bar and find the "Amazon Stickers" button on the left of the bottom bar. This opens up a menu of stickers organized by categories, and every one links to that product on Amazon. Simple. Once you place the sticker, click the "i" button to go its page. (The click-through feature is disabled when you save the image -- and then it's just a regular 'ol goofy image with a big white border.)
Seeing the internet titan try to integrate social media trinkets into its shopping app is as amusing as it is bizarre, especially since the rest of the app is dedicated to price-matching or adding items to a buy-later list. You could obviously aim the app at your empty living room and drop a product's sticker in to see how it would look, though the thick white border makes it awkward to get a real feel. It's not a terribly elegant mix of Amazon's product-hunting app and conversational gimmick, but if you have to look to fads for new functionality, perhaps that's better than not trying at all.