What Settings?

The dial knob on every dSLR is the gate way to controlling the camera. All dSLRs have this dial to give control to certain priorities and settings. As one sets the dial to the priority of  their choice they also can change the level of each priority by adjusting it through the camera body (usually a + or - button or a jog wheel).

Below are dials form the 3 major brands of dSLR

Canon

Nikon

Sony

Even though the dials are filled with tons of options only 5 of them are truly important. If one can understand what each of these 5 setting do, then almost any desired effect or shot can be produced.

Green = Automatic

P = Program

S = Shutter (also seen as "Tv")

A = Aperture (also seen as "Av")

M = Manual

As one selects an above mentioned priority on the dSLR dial, the camera starts to act differently. For example... 

Automatic - Mode: Your camera will decide every option. As the picture is about to be taken, the dSLR brain will calculate the light and decide a shutter speed, aperture and ISO that will give a standard picture. This setting is great if a picture needs to be taken quickly and with the best possible chance of not screwing up the shot.

P - Mode: You control the exposure level and all other setting are decided by the dSLR. (You choose the ISO if AUTO ISO is turned off)

S - Mode: You control the shutter speed and exposure level but all other setting are decided by the dSLR. (You choose ISO if AUTO ISO is turned off)

A - Mode: You control the aperture and exposure level but all other settings are decided by the dSLR. (You choose the ISO if AUTO ISO is turned off)

M - Mode: You control every setting and the dSLR makes no decision.