The Exposure Triangle

Photographers and videographers must understand the relationship between three things in order to control the camera and set the exposure intentionally.

ISO - how sensitive the light sensor will be to light
f-stop/aperture - how much light is allowed to pass through the lens iris
Shutter speed - how long the shutter is left open before it closes to cut off incoming light

An adjustment to any one of these settings will impact the final exposure of the image. It is up to the photographer/videographer to set all three in balance, to achieve the desired depth of field, motion blur, and exposure.