Depth of field is the range of distance that is in focus. Using depth of field will help keep the attention on the subject by either using a shallow or deep depth of field. A shallower depth of field will make the background blurry and is useful when trying to isolate a subject. A deeper depth of field is more for taking pictures of scenery because more of the picture is in focus.
As the aperture gets narrower, the background becomes more in focus.
The pictures taken from further away had a deeper DOF and the subject became less isolated. The pictures taken close to the flowers had a shallower DOF and the subject was more isolated.
This picture is my featured image because it uses narrow depth of field. It is obvious that the background is blurry and the subject is isolated.