Retail has been undergoing a rapid, extreme time of change that hasn't happened  since online shopping came on the scene 20 years  ago. Companies like Wal-Mart,  the biggest retailer in the world, are trying to get ahead of the next trends  in how people will buy stuff. They're making a big bet on virtual reality and  augmented reality, and this week Jenny Kaplan and Lindsey Rupp take you behind  the scenes to use Wal-Mart as a case study for how you might buy a tent or even  a dress in the future.