Aperture and F Stops
This is an adjustable control that determines the width of the opening that admits light to the sensor. The wider the aperture, the more light that can reach the sensor, making it possible to take pictures in dimmer light. You can think of an aperture as the pupil of your eye. When it's bright outside, your pupils contract (and you squint), letting in less light. When it's dim, your pupils dilate.
ISO is actually a common short name for the International Organisation for Standardization. The ISO setting on your camera is something that has carried over from film. Remember back in the ‘old days’ when you used to go and buy your rolls of film and you would buy film rated at 100, 200 or 400, maybe even 800 or 1600? Well that number refers to the film’s sensitivity to light. The higher the number, the more sensitive to light the film is. The ISO bit is from the standards for film sensitivity, and the number refers to it’s rating.
So what does sensitivity mean? Well a low sensitivity means that the film has to be exposed to light for a longer period of time than a film with a high sensitivity in order to properly expose the image. With a lower sensitivity you also get a better quality image too which is why you should always try and use the lowest sensitivity you can get away with.