Buy Tomb Raider: Underworld

For Steam CD Keys, you must download (HERE), install the Steam software and create a new account. If you already have a Steam account, once you log in, click "Add a game" (located in the bottom left corner), and then "Activate a Product on Steam". After a few more clicks, you will be prompted to type in your CD Key. Thus, the game will be activated and automatically added to your account library.

GOG GALAXY is a fully optional client to install, play, and update your games. It also offers online multiplayer, achievements, chat, game-time tracking and more - but it’s up to you which features you want to use.

Use your code on the Xbox Live network to activate your games or increase your Xbox Live account's credit. To access the Xbox Live network, you need the Xbox One, a broadband connexion, a Xbox Live account, and a storage device according to your console: Hard disk drive, memory card, or USB drive.

You can download your game using the CD Key on the retailer or publisher website. Please follow the steps and instructions given by the retailer.

Use your gamecard Microsoft Points in the Xbox Live Marketplace of your Xbox 360 to purchase full games, rent the latest movies in High Definition, add downloadable content to your games. Exploit the full potential of Xbox Live!
To access the Xbox Live Marketplace, you need the following components and services: Xbox 360 Console, broadband internet connection, Xbox Live Silver membership (included in the product contents of the Xbox 360 entertainment system), Microsoft Passport account, Hard Disk or Memory Unit for the Xbox 360 Console.

To use a Steam gift game, you need to own a Steam account and use the link provided to add the game to your library.