Long story short, UV is a digital locker where you store your movie rights (proof of purchases). UV then connects to Vudu or FandangoNow in the US) Your purchases show up in both accounts. You can redeem your codes directly in VUDU, or at
https://www.myuv.com/.
Movies Anywhere is the same thing, except it connects to more retailers. iTunes, Amazon, Google Play, and Vudu. Most UV codes can be redeemed at
http://www.moviesanywhere.com/welcome, or Vudu.