A quick 3 minute video explaining what ISO is, how you should use it, the effects of ISO on an image and more.
Update: I stand corrected in one area. In the video, I suggest super high ISO’s have no place in the real world. My good mate Master Photographer, Ross Gibb from Ross Gibb Photography tells me he uses the highest levels of ISO, up to 200,000+ with a super fast shutter speed for night based motor sport and especially drag racing, to get the best effect from the artificial lighting.
Example below