From the Home Screen on your XBOX One, navigate to the XBOX Store and select Browse apps, then go to Search apps and look for HBO GO. Select the green Install button to download the app. You can launch HBOGO from here after the installation process. Once installed you can also find the HBO GO app under "My Games and Apps" on the XBOX One Home Page.
To view the content of the HBO GO app, you will need a subscription through the Apple App Store or Google Play Store, or by subscribing to a package with a participating service provider.
You can currently access to HBO GO on XBOX One in Mexico, Colombia, Argentina, Chile and Brazil.