The non-working copying might be cause by the "Paint under" blending mode. The blending mode (Paint over, Replace, Paint under) influences the pasted image - look for 3 icons with red-over-blue rectangles.
Another problem might be that you are copying part of an empty layer. Only content in the active layer is copied.
Cloning tool icon looks like a rubber stamp. BTW you did not specify what software you are actually using - cloning is currently only available in RealWorld Photos.