When you're eating out at a restaurant, chances are you'll find somebody snapping a photo of her food. Most likely, that picture would be uploaded to several social networking sites she's on. In a few minutes, that post would receive comments, likes, retweets or repins. When she has finished her meal, she'll most likely respond to those who paid a compliment.
Can you see what's happening here? That's user engagement achieved through the power of social media and mobile. The same concept can also be applied to your business.