This app captures surface details of whatever you can shine a light at. Previously, there have only been a handful of devices in the world that could retrieve these details, mostly for game development or archeology, but now your phone can too.
The app functions by taking pictures in controlled lighting environments. To do this, all you need is a selfie stick and a light, but there are other ways. As long as the phone is stable, and you can take pictures of your subject while shining a light at it, the phone can get the surface details through a "normal map" - a special blue and purple image that has topographical information of whatever you took a picture of.
The phone then renders these pictures, and the app ties the renderer to the gyroscope - so turning the phone around turns the light around, and it looks super realistic, if done right, so good luck capturing those normal maps!