Too many users never realise what the default configuration entails on their Nikons. This again leading, inter alia, to nonsensical statements about the aperture ring being superfluous or non-functional on a modern Nikon. All modern Nikons except the most lowly D3xxx-D5xxx models support the alternative configuration in which you are are allowed to set aperture directly on the lens (if the lens has an aperture ring, of course; otherwise, the camera falls back to "G" lens mode).
One additional reason for getting "stuck" on a single aperture is the camera is in P program mode, thus changing the shutter speed not the aperture value.
