Nikon D90 Exposure Modes Part 3 “Advanced Modes”
Manual (M) – Every setting is selected by the user for the ultimate in photographic creativity experience.
Aperture Priority (A) – Choose this mode to control sharpness and how much of your image is in focus, depth of field. You select the f/stop and the D90 will automatically calculate the shutter speed.
Shutter Priority (S) – This mode is mostly used for freezing action or creating blurr effects. You select the shutter speed and the D90 will calculate the f/top automatically.
Program (P) – In this mode the D90 calculates many of the settings for proper exposure. These setting however can be overridden by you the camera operator. This mode is a good first step away from auto mode.