The Prize Wheel is an alternative of buying packs for those that don't have a lot of coins. It was released on the version 1.12.1 and was in replacement of the daily gift. What is very nice with this feature is that you can "Shuffle" unlimited time the blocks that you can get. Once you are ok with that, you just have to press the "Spin" button and wait until it stops on a block or texture. You have only one free spin per day, but if you want more, you first have to pay 10 coins, and then 25, 50, and it goes higher and higher. The price will reset each day. (As of the 'Player Marketplace' update, every spin [excluding the daily free spin] will only cost 10 coins.)
The only problem with the Prize Wheel is that you can't have all the block or texture, most of them are only avalible by buying the packs.
As of the 'Christmas 2015' Update, blocks you can't normally find in sets (Football helmet, Football armor, etc) are available in the spinner.
As of early 2017, the prize wheel has a new look, and now there is also a lucky prize wheel to win rarer blocks.