ISO
For digital photography, ISO or reactivity of the camera is the sensitivity of a camera’s sensor or “the active pixel sensor”. What us it sensitive to though? that would be light. A camera with a small iso value like 100 would be a low sensitivity to light and therefor making the picture less bright.
Shutter speed.
Shutter speed is a camera’s ability to capture and freeze action. a fast shutter speed would make it easier to capture something moving like a cat or a flower in the wind. a slow shutter speed on the other hand would be better for taking photos of things that never move like a wall or a person holding still. cameras in the past had a slow shutter speed and could only capture what was not moving. That is why one of the first pictures looks like an empty street because the shutter speed was not fast enough to capture any people who were walking down the street.
This picture is a good example of slow shutter speed because you can see the signs and market setups, but all of the people are blurred.
Aperture.
Aperture is what would blur the background of a photo. It is the space in which light travels making the focus of the picture more obvious. The larger the hole on the camera is, the more focus it will put on the closer item, the smaller on the other hand will make the whole image clear and obvious to the observer.
This image was taken with a wide aperture setting because the background is blured and the main focus is the beetle.