Sharpening & Softening
In conventional photography an image is either sharp or unsharp. There is not much that can be done about that. In digital photography however, there are several options to make an image sharper or softer by enhancing or blurring edge detail to make boundaries between darker and lighter image tones more or less prominent.
Raw images produced by digicams often have a certain softness to them. Some digital cameras then apply a built-in sharpening function, often to counteract the effects of interpolation.
As the adjustment of in-camera sharpness levels is usually rather limited, jaggies or artifacts can become more visible. It is better to leave sharpening until after adjustment in your digital darkroom. Unsharp Mask is the tool to use, since this allows the most precise adjustment levels and has a wide variation of parameters to produce the exact effect you need. Failing this, using the in-camera function would be your only option.
Not every subject will need an equal amount of sharpening and some subjects are best left a bit soft. Female portraits will usually benefit from slight softening to make their facial features more flattering. Also if you want to blend your image into a background or paste them into another image, it is best to soften edges a little to make their borders less prominent so that joints between parts of an image become invisible.