Aperture

Almost all automatic cameras today have some sort of preprogrammed shooting modes. These are designed for specific situations such as action, landscapes, and portraits. If you know what these modes change about your camera settings you can use them to your advantage in many more situations than just the intended ones.

Macro
Macro mode is an automatic setting mode where the camera is predisposed to use the large aperture to compensate for the DOF compression of close-up shooting. In this mode you can not set the exact aperture you want but you can lessen your chances of an out of focus close up subject by using this mode.

Landscape
Landscape mode is basically a large DOF mode. Landscape is programmed to give the smallest aperture (largest F-Stop) possible in order to ensure a large depth of field. This means that the shutter speed will be slower. If your camera does not allow Manual or Av mode and you are wanting to shoot a subject where the background is in focus, try the Landscape setting.

Portrait
Portrait mode uses a large aperture to create a small DOF. Portrait is programmed to have a shallow depth of field (large aperture/small F-Stop) and use a slow film speed in order to throw the background out of focus and obtain a very fine film grain. Use this setting anytime you want a blurry background.