The Aperture of a lens shows how much light the lens lets in. The aperture size will regulate the film’s or image sensor’s degree of exposure to light. A fast shutter will require a larger aperture to ensure sufficient light exposure. Also, a slow shutter will require a smaller aperture to avoid excessive exposure
The larger the aperture, the more light is let in, conversely a smaller aperture lets in less light. Measured in f-stops, these are inverse values, as shown in the aperture chart below, the larger the aperture the lower the f-stop number. An aperture of f/2 lets in more light and shallow depth than an aperture of f/32.