The Sharpen tool focuses soft edges in a photo to increase clarity or focus. Oversharpening a photo gives it a grainy look. You can avoid oversharpening by setting a lower Strength value in the options bar.

What does the Sharpen tool do?

The Sharpen tool in Photoshop Elements increases the contrast among adjacent pixels to give the illusion that things are sharper. This tool should be used with restraint, however. Sharpen can quickly give way to overly grainy and noisy images if you're not cautious.

How does sharpening an image work?

It subtracts a blurred (unsharp) copy from the original image to detect any edges. A mask is made with this edge detail. Contrast is then increased at the edges and the effect is applied to the original image. While unsharp masking was originally a film technique, it's now the basis of digital sharpening.