How do you control Aperture, Shutter Speed and ISO?
While most serious cameras have a manual mode where you control everything, it's usually not the best idea unless you're shooting in a very controlled, studio type setting. You're best off controlling either Aperture or Shutter speed and letting the camera control the other. If you're using a DSLR, then you'll perhaps know the modes to control these as Aperture priority (A on Nikon, Av on Canon) and Shutter priority (S on Nikon, Tv on Canon). All you need to do is pick the parameter you want to control, select the ISO you're willing to live with and let the camera help you along from that point.