What does it mean to take a line from the photographic aperture?

When shooting, adjust the aperture of the camera and reduce the aperture by one notch. The aperture of photography is an adjustable hole in the middle of the lens to control the amount of light entering the camera. When the aperture is reduced by one step, the total light input is reduced and the picture is darkened by one step. When the aperture is enlarged by one level, the total amount of light entering increases and the picture is brighter by one level.