Thanks everyone for the suggestions on the manuals. I knew the resource reported by Alain and, of course, that of Joaquín, whose translation into Italian I have completed, but not yet refined.

However, I didn't know the file reported by Mikael, which I found to be an excellent tutorial to get started with.

The documentation on ConTeXt is copious, and we know it: just look at the manuals on Contextgarden. But it is decidedly fragmented, and this disorientates the user.

I believe, therefore, that what the community misses is a tutorial/reference manual/complete guide that comes directly from the ConTeXt team (Hans, Wolfgang, etc). And, above all, that it is up to date: on Contextgarden many ‘valid’ manuals date back to many years ago, and the obsolescence of the software guides could make people say something like «well, stuff from years ago, I don't trust it».

A manual in a single file that has, in short, the seal of officiality: the various resources in circulation are just as many excellent efforts by individuals, who however have put their own approach to ConTeXt into their work. Perhaps there is a more correct approach than others, more essential, which is worth knowing.

I am speaking to you as a LaTeX user, and therefore I may have written a lot of nonsense in my message.
I conclude by saying that, in the end, the ConTeXt team may not be interested in all this, and therefore our discussions are pure academic. :)