Exposure compensation or Exposure Control is used to alter exposure from the values chosen by the camera.
Often a composition has widely varying intensities of light. To get a good exposure in these tricky situations, don’t use the histogram (which shows the distribution range of pixels from black to white) but rather look at the highlight warning alerts- the “blinkies”. Any area which is blinking shows it is so severely overexposed there is no detail. Use this button to override the camera’s exposure by darkening the exposure a bit until the detail returns. Push the button down and rotate the main wheel to reduce the exposure.
PS: shutter speed and aperture don’t change.