Once you shoot a photo, Sprinkles will offer you a few suggestions based on what it sees in the picture. For selfies, it'll offer you up some automatic "photo booth" style props using face detection. It can also guess your age, a trick that Microsoft's been showing off for some time now. Other options include having it match your face with that of a celebrity or offering some default captions based on the content of the photo, your location or the day of the week (for some reason this app has a real beef with Tuesday). Some of the options are based on seeing a face, with captions to match.
If you want to get more custom, you can write your own captions; as expected, there are a handful of different fonts and colors you can use. You can also drop emoji and stickers into your photos. There's a pretty detailed sticker search option that offers a few suggestions based on what's popular and what it detects in your photo. Those suggestions don't feel terribly relevant at first glance, though. Sprinkles identified one selfie I shot as a "close" photo (because it was close to my face) and the resulting suggestions for stickers and emoji were basically nonsense, including umbrella and mailbox emoji.
Still, this app is just meant for goofy fun so I'm not going to be too hard on it. Being able to swipe through some suggested edits for your pictures is definitely fun, although Microsoft will need to increase the variety it is showing off pretty quickly or else this app will be a one-trick pony. If you want to give it a shot yourself, it's live in the App Store now.