According to wikipedia.com; vignetting (vin-ye-ting) is a reduction of an image's brightness or saturation at the periphery compared to the image center. A similar effect occurs when filming projected images or movies off a projection screen, the so-called hotspot, defining a cheap home-movie look where no proper telecine is used.Although vignetting is normally unintended and undesired, it is sometimes purposely introduced for creative effect, such as to draw attention to the center of the frame. A photographer may deliberately choose a lens which is known to produce vignetting. It can also be produced with the use of special filters or post-processing procedures.
OK, I am not sure about you but that is about as clear as a muddy stream. However, with all that stated we are going to look at vignetting in a creative and positive manner to create focus. In the first example, I used Lightroom to darken the edges which created an interesting effect to the image. This effect causes our eyes to focus on the center of the image. In the second example, I lightened the edges which caused a framing effect. This pushes our eyes to the center of the image and changed the look of the image.
I use Lightroom to create both types of effects. However, this can be done in Photoshop and no doubt Photoshop Elements. Experiment with a copy of one of your images.
In the final image [which is one of my favorites] I lightened the edges to cause the focus to fall on the mom and her baby. Lightening the edges does not match the wikipedia definition but it causes the eyes to focus on the subject. I use both types to create a 'different' look to an image. Experiment and see what effects you can create.