I want to write the manual for an open-source software. As the manual will contain several pages I considered texinfo the best option since the manual will be too long for a man page and the user should be able to open it in a ssh session.
However, I can not find a good tutorial or manual and the official documentation is too cryptic. Can you share a tutorial or manual about texinfo?
texinfo is a TeX format to typeset files in the GNU info format, so you are looking for a tutorial of that format. GNU info is documented in its own format, so a starter is the command
info info
on a GNU/Linux computer.