GIMP and many other image edit and creation software provide too many features to be able to condense "the basic operating procedure" into a few paragraphs.
That aspect that makes these programs useful also make them complex enough that specifics are usually the only way to accomplish a task. As an example, a friend desired to have step-by-step instruction for green screen compositing using GIMP. Together we created a document with example images which would enable almost anyone to perform an entertaining image creation.
To prevent confusion, it was a rather verbose document, not unlike my replies. When completed, it spanned fourteen pages in 12 point type in MS Word! That was to accomplish a single specific goal.
GIMP is far more capable than that one task and would require volumes to cover everything.
Like you, I desire often to have a good overview of a particular program in order to better grasp the possibilities. Such an overview might provide for easier learning as well, but I've found these overviews to be non-existent.
It is typical for online tutorials and published documents/books to present a project for practice, covering the specifics of the task. From performing each individual step of the project, one is expected to learn how the step interacts with the project, but also one is expected to expand from this understanding and apply it for future projects.
That aspect of documentation is lacking in most instances. I would like to see, in the above described example, what happens if something goes wrong, but also how one might apply a particular feature to a different project in a different form.
Of course, such a document or tutorial quickly becomes excessively large and impossible to absorb.
Thanks to internet resources with respect to tutorial videos and supporting posts, one should be able to find an answer to a task, using specific directions, but then it's up to the viewer to learn to apply such information in the future.