Exposure Triangle

Shutter Speed- Aperture- ISO

Shutter Speed

The shutter speed is what determines how long the shutter remains open as the picture is being taken.
How To Set Shutter Speed for DSLR Video

Aperture

Aperture is the amount of light being let into the camera.
Video Basics: Aperture

ISO

ISO is the level of sensitivity of your camera to available light.
A Simple Explanation of ISO for Digital Photography and Video