The three elements are:
1. ISO – the measure of a digital camera sensor’s sensitivity to light
2. Aperture – the size of the opening in the lens when a picture is taken
3. Shutter Speed – the amount of time that the shutter is open
The intersection of these three elements is where an image’s exposure comes from. A change in one of the elements will impact the others. This means that you can never really isolate just one of the elements alone, and should always consider how the others will effect it.