Understanding Aperture

Small Depth of Field

 ISO- 800
Aperture- 5.6
Shutter Speed- 1/200

 Large Depth of Field

ISO- 800
Aperture- 11
Shutter Speed- 1/50

1.  Aperture is the window.  It is how much you are seeing through the camera.  Aperture also controls the focus of the camera.
2.  In a camera aperture controls what is focused and what is not.  It controls whether there is a large depth of focus or a small depth of focus.  In a photo it controls what is blurry and what is not.  For a small depth of field the subject is focused and the background is blurry.  For a large depth of field the subject is out focus and the background is focused.
3.  When changing the aperture you have to change the ISO and the Shutter speed to adjust to the changes in Aperture.