The Touch Up tool allows you to paint one part of an image over another part. This can be used to remove scratches, blemishes, or even entire objects from a photo.
Define where the brush copies pixels over from by holding Ctrl and clicking on the image. Once you've done this, pixels from the source point will be copied into your brush strokes. You can redefine the brush source by holding Ctrl and clicking again.
Use the Size: slider to adjust the brush size.
Use the Hardness: slider to adjust the brush hardness. A low value will give brush strokes soft edges, and high values will give brush strokes sharper edges.
Use the Strength: slider to adjust the brush stroke transparency.