The clone tool is ideal for retouching images. It enables you to paint in an image using information from another part of the image. If desired, it can instead take information from a pattern.
When retouching, use a small brush with soft edges. In this way, the modifications can blend better with the original image.
To select the source point in the image, press and hold Ctrl while clicking the desired source point. Then paint with the tool. When you move the cursor while painting, the source point, marked by a cross, moves as well.
If the Alignment is set to None (the default setting), the source resets to the original when you release the left mouse button.