After you have bought your camera, you will need to know how to do several settings. This can because you will take photos in different circumstances and you need to be flexible.
One of those setting is the EV Compensation, which stand for exposure value compensation. Simply speaking, the EV compensation button on your camera allows you to darken or brighten your image in a quick way.
While the camera has a default option of exposure, sometimes they may not be doing what you are thinking of—after all, you are much smarter than the camera. Therefore, you will need to command the camera in that case.