To take a screenshot or record clips on Xbox One you have to make sure you have an Xbox Live Gold subscription, otherwise this won't work. When in-game, simply tap the Xbox button on your control pad to open the Guide and then press Y to take the screenshot. If something cool has happened and you want to grab a clip of the last 30 seconds of gameplay, press X.
Once you've got what you need, you can find it in the 'Manage Captures' menu where you'll be able to access a range of sharing options which range from your Activity Feed and private messages to Twitter and One Drive.
