"To explain depth of field, I will use two types of photography
for examples. Landscape photography and portrait photography. When
taking a landscape photograph, you typically want everything to be
in focus. To to this you will want a large depth of field. In
portrait photography, you want to focus on the subject and have the
background be blurry to not distract from your area of focus. For
this you will need a shallow depth of field.
"On a camera, increasing the f-number (decreasing the aperture
diameter) increases the DOF; decreasing f-number decreases DOF.
"Tweaking the aperture is something most people don't know how
to do (some cameras it is not even possible). One thing you can do
for this is stand back and zoom in; OR you can use the Gimp!"