Three main camera controls influence the look of any photo. The aperture, which I’ve discussed in a previous Howler article, affects depth of field. That is, whether everything front to back appears sharp or whether your subject is isolated against a smooth background. The second camera control, ISO, determines the degree of noise (the digital analogue to film grain) apparent in a digital image.
The third camera control is the shutter speed, which refers to the exposure time. Imagine shutters on a house. Open the shutters, and the window is exposed to the daylight. Close the shutters, and light no longer hits the window. Taking this analogy over to the camera, the shutters are the curtains that cover the digital sensor (i.e., the window). When you press the button to take a picture, the camera’s shutter curtains open to expose the digital sensor to the light. The shutter curtains close again to end the exposure. (Today’s smartphones and compact cameras function differently, but the analogy still works.)