"How to redeem a code on Xbox console;

Press the Xbox button to open the guide, and then select Store.
Press the View button to open the side menu, and then select Redeem.
Enter the 25-character code, select Next, and then follow the prompts.

How to redeem a code from a PC or mobile browser; 

From a web browser, go to redeem.microsoft.com.
Enter the 25-character code, select Next, and then follow the prompts."

Buy Cities: Skylines - Xbox One Edition (XBOX One)

Buy Cities: Skylines - Xbox One Edition (XBOX One)

Cities: Skylines - Xbox One Edition (Xbox Games US)

Cities: Skylines - Xbox One Edition (Xbox Games UK)

Cities: Skylines - Xbox One Edition (Xbox Games TR)

Cities: Skylines - Xbox One Edition (Xbox Game EU)

Cities: Skylines - Xbox One Edition (Xbox Games BR)

Cities: Skylines - Xbox One Edition (XBOX One)

Comments about Cities: Skylines - Xbox One Edition (XBOX One)

Recharge Cities: Skylines - Xbox One Edition (XBOX One) - Online

Buy Cities: Skylines - Xbox One Edition (XBOX One)

Cities: Skylines - Xbox One Edition (Xbox Games US)

Cities: Skylines - Xbox One Edition (Xbox Games UK)

Cities: Skylines - Xbox One Edition (Xbox Games TR)

Cities: Skylines - Xbox One Edition (Xbox Game EU)

Cities: Skylines - Xbox One Edition (Xbox Games BR)

Cities: Skylines - Xbox One Edition (XBOX One)

Comments about Cities: Skylines - Xbox One Edition (XBOX One)

Recharge Cities: Skylines - Xbox One Edition (XBOX One) - Online

Information