Depth of field

Nikon AF-S DX Zoom-Nikkor 18 - 55mm f/3.5 - 5.6G ED

First, set the camera to the A setting for aperture priority mode.
As you change the aperture, shutter speed is automatically changed to a correct exposure.

Aperture settings affect depth of field (DOF).
The diameter of an aperture is measured in f-stops.

Large aperture (smaller F-stop number)
More light gets into the camera.
The depth of field will decrease.
The range of the flash will increase.
Backgrounds will be tend to be soft but not blurred.

shown: f/3.5-22 [18mm]

Small aperture (larger F-stop number)
A smaller aperture causes a greater depth of field
Less light gets into the camera, requiring longer exposures.
Flash range decreases.
Backgrounds outside the depth of field range can be blurred.

shown: f/5.6-38 [55 mm]