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The light on the Xbox button will pulse off and on, which indicates the controller is not yet synced to your Xbox One.  Your controller’s “connect” button is located at the top left side of the controller. The controller will be synced with your Xbox One console when the flashing lights become solid.

Summary:
Power on the Xbox One console. Verify that your wireless Xbox controller contains batteries. Press and hold down the Xbox button on your controller to power on the controller. Press and release the “connect” button located on the left side of the Xbox One console. Press and hold the “connect” button on the controller within 20 seconds of pressing the “connect” button on the Xbox One console. Continue holding down the controller’s “connect” button until the light on the Xbox button flashes quickly.