To play your game you need to install the Uplay Client for PC on your computer, available HERE.
Once installed, log into the application using the same Ubisoft Account you've used for this purchase.
Your game will be located within the Uplay PC application's GAMES list upon completion of purchase.
Note: Preordered purchases will only be visible when a preload option is available.
For further questions regarding the Uplay Client for PC, please review the Ubisoft Technical Support website: http://support.ubi.com