I know it's real bread and butter photography kinda information, but it's a good thing to have pinned around
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
Is is at the intersection of these three elements that an image’s exposure is worked out.
Most importantly - 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 but always need to have the others in the back of your mind.