There is a need to balance between spending time spent documenting and
spending time developing (fixing bugs and adding features etc...). More
documentation and more examples in the documentation would be welcome,
but given the time constraints of Org-mode developers and contributors
not every desirable task can be accomplished.
Thanks Eric for these explanations. Again my remark is not to be understood as an harsh critic. Just a remark on a gap existing in every educational task: sometimes teachers do not understand why students do not understand. What seems very easy to some people is obscure for others who need more time and more explanations.
I am going to read your tutorial, and I thank you warmly for your help. Of course I will tell you if I succeed or if I do not.