If you are new to Battle.net then simply follow these instructions to download the software and activate your game code
Step 1. Login or Create an Account
Go to: Battle.net.
If you have an account simply login, if not then click ‘Create Account’ and follow the registration form. You may also need to confirm your email address.
Step 2. Add a Game Key
Once logged in to your Battle.net account, select ‘Account’ or ‘Account Settings’ in the top right-hand corner (or go to: https://eu.battle.net/account/management/)
Click on the green button that says “Add a Game Key” and enter your game’s product code on the following page. Redeem your code and you’re done!
Now to installation…
Step 3. Installing Your Game
Once your game code has been activated the game is added to your Battle.net account. To install your game click on the link “Download Clients”, which is located just below the green “Add a Game Key” button.
Alternatively, go directly to: https://eu.battle.net/account/management/download/
We recommend that you install the Blizzard Battle.net app and then installing your game.