The Xbox One didn't get the ability to take screenshots until the March 2015 system update. You'll need to have your Xbox One updated in order to take screenshots. You'll normally be prompted to update automatically.

If you aren't prompted to update, open the Settings menu, select "System", and then "Update Console".
 You can't take screenshots of the Xbox One menu.,, Y to take a screenshot. If you have a Kinect, you can say "Xbox, take a screenshot"., You can find all of your screenshots in the Upload Studio app, under "Manage Captures". You can then share them to various social networks or save it to your OneDrive.
Update your Xbox One.
Start up the game you want to take a screenshot of.Tap the Xbox button twice to open the Snap menu.
Press .
Find your screenshots.
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