Now that you know what Aperture, Shutter Speed, and ISO are, now its time to put it together.
One of these things is constantly forcing the other one to change. Since aperture controls how much light is going in and the shutter speed controls how long you expose the image for and the ISO controls the light sensitivity of the sensor, you have to put it all together!
The lens for this purpose is a constant f/4 lens...Lets say you have your ISO set to 400, Shutter Speed to 1/200, and Aperture to f/4. If the image appears dark when you take the picture and review it on the LCD screen, there are a couple of things you can do...one thing is increase your ISO to 800 or lower your shutter speed..It is preferable to lower your shutter speed until it is at a point you can no longer hand hold it, because the higher the ISO the more grain there is in the image...So now if the image still appears dark and you know you can't hand hold the camera steady if you decrease the shutter speed anymore, you should increase the ISO to 800
This lens for this purpose is a constant f/2.8 lens...You are taking a picture of waterfall, but want the cotton candy look (blurred water). First thing you should do is put your camera on a tripod, because you just can not hand hold this upcoming shot. Next you should set your camera to f/2.8, ISO 400, 1/10th SS. Now take the picture and examine it. if the image is coming out way too bright, increase the f-number to around f/8...Keep experimenting with the f-number and if you just can't find an f-stop that makes the shot not look too bright, decrease the ISO to 100 and take a shot, if it looks too bright, you have to increase the f-number. Now if the water just doesn't look blurred enough, you have to lower the SS and then reconfigure the ISO and f-number again