controls the amount of light that enters through iris in the lens and is measured in f/stop , you can adjust this by changing said f/stops.

Depth of field is defined as what is in focus in front and behind the subject , shallow depth in field has limited things in focus often with a blurred background this requires f/stop of f/2 or f/4. Depth of field is defined by aperture the higher the number the more in focus an example of this would be f/16 or f/22.

As seen here the high aperture is f/2.8 meaning the depth of field in lower keeping less in focus