ISO

This was taken with an ISO of 200. 

This photo was taken with an ISO of 6400.

Questions: 

1. This would make up for the fast shutter speed needed to shoot motion. 

2. The author suggested that you keep your ISO at base/ low to improve the quality of your pictures, but to raise it in a dark area or when taking photos with a high shutter speed. 

3. Auto ISO, Manual, Shutter Priority, Aperture Priority, and Program.