The Clone Stamp tool paints
one part of an image over another part of the same image or over
another part of any open document that has the same color mode.
You can also paint part of one layer over another layer. The Clone
Stamp tool is useful for duplicating objects or removing a defect
in an image.
(Photoshop Extended) You can also use the Clone Stamp tool to paint content on video or animation frames. See also Cloning content in video and animation frames (Photoshop Extended).
To use the Clone Stamp tool, you set a sampling point on the area you want to copy (clone) the pixels from and paint over another area. To paint with the most current sampling point whenever you stop and resume painting, select the Aligned option. Deselect the Aligned option to paint starting from the initial sampling point no matter how many times you stop and resume painting.
You can use any brush tip with the Clone Stamp tool, which gives you precise control over the size of the clone area. You can also use opacity and flow settings to control how paint will be applied to the cloned area.