very well explained, you should copy/paste this on the documentation wiki page :-)
For years openSUSE has had 2 primary documentation sources:
The first is the wiki. The second is the manuals. The manuals I assume are what used to come in the box sets.
The manuals are listed at https://en.opensuse.org/openSUSE:Documentation_List_of_Manuals
In days past the manuals were maintained exclusively by SUSE/Novell employees I think.
In order to make the "manuals" community supportable they have moved them to https://activedoc.opensuse.org
For instance the security guide is at: https://activedoc.opensuse.org/book/opensuse-security-guide
If you want to contribute to the manuals: https://en.opensuse.org/openSUSE:Documentation_Contribute