primary effect of aperture

The primary effect of aperture is to regulate the amount of light passing through the camera lens. The secondary effect is to alter the depth-of-field. It’s the same with shutter speed. The primary effect is to regulate the quantity of light that reaches the sensor when you take a photo. Learn more at http://spanishinperu.org/nantucket-wedding-photographer-2015/ and https://erinjgz.wordpress.com/2014/05/07/nantucket-massachusetts-wedding-photography/
The secondary effect, and the one of interest to creative photographers, is to do with the way that motion is captured by the camera. If you use a fast shutter speed (say 1/500 second or faster) you can freeze movement. Sports and wildlife photographers use fast shutter speeds to freeze the motion of athletes and animals in mid-movement. If you use a slow shutter speed (from around 1/30th second to shutter speeds in excess of a second or more) you can capture the movement of the subject as it passes in front of your lens. This is the technique I used to capture the steel wool spinning photo in the introduction. Both of these techniques are interesting because they enable the camera to capture the world around us in ways invisible to the human eye. We see life in continual motion, more like a video camera than a stills camera. We can’t freeze something in mid-air – but the camera can. Nor can we slow something right down so it appears as a blur rather than a sharp object. But the camera can do this as well. Check out photography at http://pommettphotography.com/
I took this photo from the top of the World Finance Centre in Shanghai. Look at the roads underneath the buildings – you will see light trails along the streets. These are created by the lights from cars as the move across the frame during a long exposure. In this case I used a shutter speed of 20 seconds (and supported the camera with a tripod).
Fast shutter speeds are required for sports and action photography. Shutter speeds of 1/500 second to 1/8000 second help you freeze people and wildlife in motion. It’s the same principle as when you see slow motion sports coverage where each frame is razor sharp and The exact shutter speed required to freeze motion depends on the speed of your subject, the focal length of your lens and the direction that your subject is moving in. The best way to see is to experiment. That’s where the camera’s LCD screen comes in handy. You can play back your images, and compare the results that you obtain with different shutter speeds. It’s a quick way of learning, and one of the benefits of digital photography.
These two portraits show how you can use shutter speed creatively to improve your photos. For the first I set a shutter speed of 1/125 second. It comfortably froze my model, and allowed me to hand-hold the camera without camera shake. But look at the water. There is some blur (the shutter speed was not fast enough to freeze the water completely), and I knew the image would be more interesting if the water was blurred even more.
So I used a shutter speed of 1/2 second for the second portrait, and asked my model to remain still for the photo so that she would come out sharp.