The aperture is located on the camera lens and effects the depth of field and the light of the picture you want to take.
The depth of field is determined on your focal ratio. The larger your focal ratio is the greater the depth of field is causing everything in your photo to be in focus. With a smaller focal ratio your depth of field decreases causing the main subject in your picture to be in focus while the background is blurry.
Now the aperture also affects the amount of light that enters a picture. With a smaller focal ratio more light is allowed to enter the picture. When your focal point is at a larger setting less light enters the picture you wish to take.
Author: Chris Heisler