mjtags,
The easiest (quickest?) way (there may be other methods) is to
- select the area to "clone" - retangular or other method
- copy it to the clipboard (Edit/Copy or Ctrl+C)
- make the other image active
- paste - into current image (Edit/Paste or Ctrl+D)
The pasted area can be dragged into position, rotated or resized. Once positioned, Selections/Select None (or Ctrl+E) will "drop" the portion and clear the selection. If the pasted portion is on its own layer, then it can be further manipulated easily.
I have been using Ultimate Paint for years, and it uses a method where the selected portion becomes a "brush". PPP is slightly different.
Cheers!