In tracker-less or surface-based AR, you can place digital content in your surrounding environment. How it works, is that the camera maps the real world into an augmented space and allows you to place your content and interact with it.
These type of experiences are different from tracker based experiences as they do not require any anchor/tracker images and you can interact with digital content in your own surroundings rather than over an image.
Such projects require you to scan a well-lit but none shiny flat surface to place your digital content. Just scan your project QR code, detect a flat surface and view your project in an augmented environment around you.