Hmmm.... *scratching head*(posted 8545 days ago)ISO is the value of film speed. A certain amount of light is needed for a proper exposure. This is accomplished via apertures and shutter speeds.
"1 stop" is the same as: -> one change in f/stop -> halving or doubling shutter speed -> halving or doubling the film ISO speed (alternate EI) -> 1 EV.
Negative film has roughly 6 stops latitiude. That means it can see detail 3 stops over and 2 stops under average grey. Depending upon your camera/light meter, this could mean physical stops in shutter speed or aperture or EV.
That being said, frame a scene and spot meter what you would expect to be average grey. Read that EV value. Then take additional readings on objects in the frame that might be in the highlights or shadows in the scene. If they fall in the +3 EV / -2 EV range of your original average grey reading, you should be able to have detail in those highlights and shadows of your photograph. If you are not happy with what you have, you could adjust what you want to be average grey and move your range of film latitude accordingly (within reason, of course). For example, if you want more shadow detail, find something in your scene that would be one EV less than your original average grey. This will then boost your original shawdow detail one stop more (rendering more detail). Also you can go the other way if you want to render a highlight more (rather than have it blown out). Once you are satisfied with your range, your can set your f/stop and shutter speed to make your average grey come out exposed properly. Shadows and highlights will fall into place.
The same can be done with using shutter speeds and f/stops. Go into aperture or shutter priority (or fixate on one or the other on your full manual camera). Play the game of metering around and checking "stops". Again, +3 / -2 stops will be what you are looking for. Touching on what James said, it can be done with f/stops and shutter speeds. Using EVs is just a little easier. You would work with whole numbers vs. halving-and-doubling everything.
Oh and by the way, you have just touched on what the Zone System is all about. It can be used as a tool to inform you ahead of time of what could be rendered as shadow and higlight detail in a photograph.