ISO is the level of sensitivity to light. the lower the ISO number, the less sensitive it is to the light. therefor the higher the ISO number, the more sensitive it is to light. a high number will be 1000+ and lower number will be 100 and under.
Aperture is how open your lens will be to light. the wider, the brighter and shallow depth. the smaller, the darker and fuller depth.
Shutter speed is the length of time a camera is open to light. the faster the speed is you freeze action and darker picture. if it is slow it can create a motion blur and it will be a brighter picture. 1/800 or 1/1000 is faster. 1/60 or 1/80 is slow.
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