AR uses live video and renders objects, while VR is fully rendered, like in computer games. AR is more common in ecommerce, because VR requires special equipment like glasses.
AR ecommerce uses include:
Virtual try-on solutions for clothes, makeup etc.
Preview placement to visualize how an item such as a couch looks in your home before buying.
Interactive user manuals to understand how a product works or how to assemble furniture.
AR is also used in social media filters. When used in phones, it requires a set of sensors (accelerometer, gyroscope, magnetometer) and fast processing (CPU, GPU). It also needs to combine lighting, camera position, and surroundings to create a quality customer experience.