This index measures the cost of option protection (insurance). It trades in the futures market (CBOE). That means it has a spot price (today) and a futures price (next month, and the next month, and so on)
To make it accessible to stock traders, several products (such as VXX) have been created. VXX is normally in contango. That means the price today is less than the future price. You lose money because when it rolls to the next month, you sell low and buy higher.
During market downturns, VXX goes into backwardation. You make money since you sell high and buy lower as it rolls to the next month.
BUT BACKWARDATION ONLY PERSISTS TEMPORARILY!
To make $$$, you must own XIV. This product is the inverse of volatility.