First, download the uPlay launcher to your computer. ( https://uplay.ubisoft.com/en-GB) You can click the “Download now” button to download the launcher.
Create an account and after you enter the launcher, click the “Games” section from top menu.
Click the "Activate a key" that located on the bottom side of the new window.
And then, enter your key which is given on the orders page of eTail.Market and enter the code to the “ACTIVATION CODE” area and click to the “Activate” button that located at the bottom right corner of the same window.
Finally, follow the steps showed and load the game to your computer. Now you are ready to play the game!