Clone stamp is used for removing unwanted objects, removing artifacts, erasing background, removing photobombs, and etc.
It can also be used for removing unwanted shadows ( especially background shadows ) , acne, mole, blemish, pimple, and skin marks.
It can also be used for duplicating, cloning, an object in a photo.
It works well when another part of the image has similar texture to be used as donor. If so, you can clone the similar texture from the other part into the affected area.

Please refer to the user guide about how to operate this app:
http://perfecthorizon.superthz.com/2019/10/user-guide-for-clone-stamp-first.html