Buy a photography book - it will tell you all about the settings you need to know. In fact I can put it in a nutshell for you here and now - save you £3000. Buy me a beer.
A 'correct' exposure is a bucket of water full to the brim, just. You can fill that bucket through a big tap for a shorter time (wide open aperture at fast shutter speed) or through a smaller tap (small aperture f8, f11, f16 etc over a longer period of time (slow shutter speed 1/4, 1/2, -1/60, 1/125 and 1/250) You don't HAVE to fill the bucket to the brim and letting water spill over is a waste of water and it runs down the drain never to be recovered (water is taking the place of light) - lost water is the same as lost highlights through too much exposure. It is ALWAYS better to underexpose, because you can recover the shadows.
Aperture - controls the depth of focus. Smallerer the number, biggerer the hole in the lens, less the depth of focus.
eg. f2 = large hole in lens, gives very limited / critical focus. Ensure eyes are focussed, f8.0, f11, f16....small hole in lens, more subject in focus eyes and nose can be rendered acceptably sharp. If you want to see this in practise with your own eyes - look at a object at about 6 feet away, clear of the wall behind (another 6 ft at least) You see yor object sharp, but the wall is fuzzy in your vision....now squint (close the aperture in your eyes) and watxch how everything becomes sharoer, BUT IT ALSO BECOMES DARKER - so if you 'squint' your lens by stopping it down, more comes sharp, but you have to leave the tap on for longer to brighten it up a bit.
The effect of this aperture relationship is also dependent upon two things: lens focal length, focussed distance. Long lens gives less depth of focus, (hence medium /short telephotos generally used for portraiture.
Wider angles provide greater depth of focus, even at close ranges. The closer the subject to the camera (regardless of focal length) the LESS depth of focus - the more critical the amount of subject is sharp. Background goes to mush.
Rule of thumb: Focus will be deeper behind the subject than in front...by a ratio of from focussed distance to 1/3 in front, 2/3rds behind. This si true at all distances and f numbers. The RELATIONSHIP stays the same, only the AMOUNT changes with lens choice, and f-stop choice and subject distance.
Aperture controls FLASH - not the shutter speed, provided it is synchronised. You set your lights for the chosen aperture. It will work with all synchronised shutter speeds.
Shutter speed - controls the ambient light entering the camera. It also has an effect on the rending of blurr for motion, or stopping motion dead through the use of high speed exposure (can also be done by speed of flash, but the amount of flash needed will controlled by the aperture and the power available as above.
FAST shutter speed - 1/500 and shorter duration (1/1000, 1/2000 etc) freezes motion, doesn't leave long to allow light through the lens.
SLOW shutter speed 1/15, 1/30 - 1/125 will not stop motion to the same extent or will even allow some blur to occur - moving hands for instance, dogs legs when running.....the feet will disappear and look like they have been amputated.
ISO - gives you the amount of light capture to use bigger f-numbers or faster shutter speeds. RULE OF THUMB (rapidly being thrown out by modern camera ability) lower the number, greater the quality. So in the olden days, when I used to have to kill a sabre toothed tiger before going out to take photographs...we had Kodachrom at ISO 64 or Fuji Velvia at ISO 50 (no, not 640 or 500, but double digits only). The standard portrait film speed was 160, except Fuji worked on solid numbers of 100, 200 and 400 (800 hadn't been invented yet, not for colour) LUXURY was having 160 to work with. You had bigger cameras with lenses the size of a drainpipe to work with too.....so we had big, heavy cameras with cumbersome lenses and no autofocus and slow speed film....it was a wonder anyone ever got a picture really wasn't it.
Choose your ISO according to the amount of light available, whether that is your own light in a box (flash) or natural light given to you by nature....
When mixing natural light with flash - natural light is controlled by the shutter speed. Flash light is controlled by the aperture - so effectively, you can turn the sun off by using a fast enough shutter speed (rendering the natural light under exposed - but provided your flash output matches your aperture the subject hit by the flash will be 'properly' exposed.
That is settings covered...how much were you going to pay a smudger for that As I said, buy me a beer. If you really didn't understand that - DO NOT THINK OF TRYING TO MAKE A LIVING FROM PHOTOGRAPHY.
