Aperture defined as the lens opening size as pictures are being shot is measures as f-stops. If the number of f-stops is low, the lens opening is large implying more light into the camera sensor and when the number of f-stop is large, the lens opening is small hence less light gets into camera’s sensor.

Aperture is used to control the picture’s focus. The larger the f-stop the bigger the field’s depth and hence more focus that results in clear pictures.