Aperture and Depth of Field

Aperture

Aperture - refers to the lens diaphragm opening inside a photographic lens. The size of the diaphragm opening in the camera lens regulates the amount of light passing through onto the recording medium inside the camera. 
The size of an aperture in the lens can either be fixed or an adjected form, like an SLR camera. Aperture is usually calibrated in f-numbers. 
Aperture and Shutter Prority modes are really semi-manual, or semi-automatic modes that give you some control over the camera and the image achieved. 

A Large Aperture = Small Depth of Field

Shutter Speed/Aperture

Shutter Speed > Time - How long the Len is open for.

Film Speed (or ISO) = Quatily of Image. 

                                    Slower the reaction = Better the image 

B - Blub 

(1 Second) 1 - 60

(1/2 Second) 2 - 125

(4/3 Second) 4 - 250

(8/4 Second) 8 - 500

15 - 1000