The shutter speed controls how much light enters the camera - the higher the shutter number, the less light; the lower the shutter number, the more light. While the aperture can adjust the light, the shutter speed also impacts it and should consider motion to avoid blurry photos from moving subjects.

10. Shutter and Light
•The higher the shutter number (2000) the less light you
have in the camera.
•The lower the shutter number (2) the more light you
have in the camera.
•If you can’t let enough light into the camera using the
aperture, you can adjust the shutter as well *but
consider motion also.