The exposure triangle

The exposure triangle                                           

Shutter speed 
Also so known as exposure time it is the length of time
the camera shutter is open to the exposure of light
if the shutter speed is fast it takes a still image
a slow shutter speed creates more of a motion blur

ISO
In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds.

Aperture
Aperture is the depth of field. Lower the number the more blur. higher number more depth of field 

The exposure triangle is the the three main elements of exposure, they're shutter speed, ISO and Aperture