Aperture- Is the amount of light that is allowed into the camera. It acts like the pupil of the human eye.  The larger the aperture the more light is allowed to enter.

Shutter Speed- Shutter speed controls the amount of time the shutter remains open which thereby controls whether the image is viewed as a motion or a still picture. The longer the shutter speed the more blurry or "in action" the photograph looks and the shorter the shutter speed the more the picture looks like a still picture.

ISO- ISO is the level of sensitivity a camera has to light. A lower ISO number correlates to less sensitivity to light.