Blood Shards are the new currency implemented in the Reaper of Souls. They can be obtained in the Adventure Mode by performing and completing one of the two activities: Bounties or Nephalem Rifts. It is much faster to get them through the second way, for the Guardians will drop several dozen Blood Shards. In the case of Bounties it is better to take those with bonus that gives you twice as many Blood Shards.
You can spend your Blood Shards at Kadala, a new trader, who appears in all of the camps. The players refer to trading with her as a gambling, and indeed, this process has a lot in common with it. As opposed to the other traders, Kadala won't allow you any insight on items you are buying. They are only divided by category (weapon, chest piece, pants, etc.) - it's a blind purchase and only after spending your Blood Shards you will learn if the purchase was of any worth.
So far Blizzard has not revealed any percentage chance to draw a specific item class (like a legendary), so we won't be able to give any certain data. What we do know, however, is that recently the price for each item was increased, but at the same time the chance to draw out a legendary item was SIGNIFICANTLY increased as well. How does it look? It depends. Some people claim that they have acquired a lot of legendary items from Kadala, while the others say that they are hardly getting any. Gambling is all about the luck, but it's definitely worth a try, as it's the easiest and fastest way to get your desired equipment!