Well, let's take a quickie stab at this... METERING: This is measuring the light available (or supplied with artificial sources, like a flash) and making adjustments to the shutter speed and the aperture (the opening inside the lens that allows light to pass through). Since the camera doesn't know what you're taking a picture of, manufacturers "calibrate" the meters to average what you're shooting to a medium tone (18% grey, to be exact) - this usually balances the light areas and dark areas of your photograph to give a good exposure. For the most part, all of this is handled automatically...it's when you start shooting stuff like polar bears in snowstorms and black bears on black lava that the meter starts having a hard time. (I'm sure you've seen indoor shots of people standing in front of a window, and the people look really dark - it's because the camera's "metering" the outside light, which is much brighter, and making settings based on that....and get this, the correct exposure for the moon is the same as on a sunny day here on earth (maybe opened up a bit to give that "glow"), but if you think about it, the moon is a "sun lit" object and needs to be exposed as so. ISO: This stands for "International Standards Organization (took the place of ASA - American Standards Association) - and refers to the light sensitivity of film. A film with an ISO rating of 400 is twice as light sensitive as a film rated ISO 200 (meaning it can produce the same exposure in half the light) - the trade off...higher speed film yields more grain (the "noise" you see in some photos). To be honest, how this translates to a digital camera, I have no clue...? Aperture: Ahhh...now we're taking the step from "shootin' snapshots" to "taking and controlling photographs". The aperture is the opening inside of the lens (just like the iris of your eye) - it controls the amount of light allowed to strike the film. The aperture, in combination with the shutter speed (which determines the amount of TIME the light is allowed to strike the film) determines the EXPOSURE (dependent on the ISO of the film). The "visual" function of the aperture is to determine the "depth-of-field" of your photograph - that is, how much is in focus, from near to far. The larger the SIZE of the aperture, the less depth of field you have. For example, if you wanted to take a portrait, and you wanted the background to be a blur around a sharp subject, you would choose a LARGE aperture (which is actually a SMALLER NUMBER - more on that in a bit) - if you were shooting a landscape and wanted the tree in front of you as well as the mountains in the background in focus, you would use a SMALL aperture (LARGER number). The actual numbers derived come from a fraction of the physical opening of the aperture relative to the focal length of the lens - i.e., with a 50mm lens, if the lens opening is 25mm, that would be f2.0 - if the lens opening is 5mm (roughly), that would be f11) Think of it as "squinting" to make an image more readable - you're making your aperture smaller to bring more into fucus. Now - you want to adjust your aperture to create the depth-of-field you want in your photograph - let's say you're making it smaller (bigger number) to get more in focus....the fact that you're making your lens opening smaller (or "stopping down") means that there's less "amount" of light allowed through the lens, and this has to be adjusted for....how?...by slowing your shutter speed down. OK - now I've had several beers, so you must forgive misspellings)....but now HERE'S where it gets a little easier, so let's talk about STOPS. Stop: This is a doubling or a halving of a value - such as light - a STOP in photography is halving or doubling the light gathered by the camera, each SHUTTER SPEED is a change of one STOP (1/250 sec is HALF as much light allowed as 1/125 sec) - and f8 is half the amount of light that f5.6 would allow (if you were thinking f4 (half the NUMBER) - that would be twice the amount vertically AND horizontally - four times the amount - I know, it's weird, but that's the way it is) f5.6 allows TWICE the MOUNT of light through as f4.0.. This is an extremely complicated way of defining your questions - but the questions you ask are the very BASIS of controlled photography - EVERY exposure is a combination of SHUTTER SPEED and APERTURE (coupled with film ISO) - it's the combination of the two (three) that give a photographer CONTROL over what he/she wants to convey in a photograph. Automatic modes in a camera are fine, so long as there's a basic understanding of WHAT THE CAMERA IS DOING - meaning, for every correct exposure, there are SEVERAL different ways to achieve/present it (1/60 sec @ f16 is the same EXPOSURE as 1/500 sec @ f5.6). There is a RICIPROCAL relationship to shutter speed and aperture, cut one by one stop / double the other by one stop - and it equals out. Anyway - I have had MUCH too much to drink but I hope I have not complicated matters. Photography is not all that difficult (technically) - shutter speeds, apertures and film speeds. The correct shutter speed at the appropriate aperature (with a given film speed) - and you've got it made! (OK - this is a bit errrr... - overstated - but it IS the basis of PHOTOGRAPHY that MOST PEOPLE overlook. (the happy "dumb-luck" of a pictue does NOT make a photographer - CONTROL of a scene/image IS! Hope this helps - Marc