Basic retouching of photos includes lightening and darkening areas of the original photograph to balance out the exposure, also called dodging and burning. It also includes erasing dust spots and covering up skin blemishes.
An optional vignette can also be added to the photograph.

The original photo, untouched and unedited.

Retouched photo, dark face and front of dressed lightened.

A black and white version of the retouched photo. In addition to retouching this version has had artificial vignetting added, or darkening of the corners.

A sepia toned version of the retouched photo. In addition to retouching this version has had artificial vignetting added, or darkening the corners.

This is the lightened photo untouched.

Not that she needed it, but her face was smoothed out a little and a few marks were covered up.