This is the exposure triangle. To get a good shot you need to take all 3 corners into consideration. ISO is how sensitive the cameras lens is to light. Aperture is how small or big the opening of the lense is. shutter speed is how long the shutter is open for. an example of how this works is, if your camera lens is very sensitive to light then you need a higher aperture like f/22. The higher the aperture, the less light it lets in. finally you would need to make the shutter speed quicker so that it lets less light into the shot.