By choosing how much depth of field to have in your shot, you can focus the viewer’s attention in a specific place. This makes depth of field control one of the most important creative decisions that a photographer makes. Depth of field is controlled by changing the aperture setting on your camera. You control the size of this hole, or aperture, by changing the aperture setting, which is measured using a scale of f-stops. the larger the aperture, the shallower your depth of field will be, meaning a smaller portion of your image will be in focus.
Aperture determines how much light can pass through a lens at a given shutter speed. A number of blades inside the lens move so that the opening they create changes in diameter. You might also want to use a wider aperture when you want to isolate specific subjects from their backgrounds. As you make your aperture smaller, you need to have a longer shutter speed in order to let the same amount of light through to the sensor. Most cameras allow you to adjust this through a control on the body, some lenses have a physical ring around their barrel.