Not really ambiguous. If you have problems following a block of text, write it down in your own words one operation at a time.
1. Duplicate the layer and sharpen,
(you can use unsharp mask or maybe wavelet sharpen if installed)
2. Use the clone tool in
registered mode
(Bottom of the clone tool options is a drop-menu with options none - aligned -registered - fixed. Registered mode will clone to the same position between layers/images)
3. Set the Opacity to a small value.
(That could be ambiguous, but not the brush it is the duplicate layer opacity, it will allow the original layer to dominate)
4.
ctrl-click on the copy to set the source.
This is nothing special, it is the way to set the area to copy, whatever mode the clone -tool uses)
5. Paint on the original layer.
Nothing ambiguous about that. the top layer is copied into the bottom layer which reinforces the overall image. What is not mentioned is the brush, usually a fuzzy brush is best with the clone tool to prevent hard edges.
screenshot:
My advice, instead of trying to find fault all the time, spend a bit more on actually using Gimp. Experimenting is a really good way to discover the functions and no matter how long you have used Gimp, there is always something new to learn.
However, keep the questions coming, someone will answer, time permitting.