The film advances automatically in many cameras. Controlling the light. To take good pictures, a camera must let the proper amount of light reach the film. The speed of the shutter's opening and closing determines how long the film is exposed to light. The size of the aperture determines how much light reaches the film during that time.
Many cameras also have an adjustable aperture.
The various sizes of an aperture are often called f-stops. The settings for shutter speed and aperture are interrelated. To let in enough light during this brief time, you would need a large aperture. Now, suppose you wanted to photograph a sweeping landscape. To bring into sharp focus all parts of the landscape that were at various distances from the camera, you would need a small aperture.