Koop SimCity 4

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 game code. Thus, the game will be activated and automatically added to your account library.

For Origin CD Keys, you must download and install Origin (HERE). Then start the client, sign in, and go to settings in the upper right corner Redeem Game Code and just enter your serial. Thus, the game will be activated and automatically added to your account library.