I read docs, properly installed and added an author (contributor on g+ set as well). But nothing is shown, even if I try to see by "view source" with right-click on the page through chrome browser, I don't see any "schema.org" tag.
Where do I make the mistake?
The simplest way is to install the template overrides for com_content.
However, if you don't or you can't install them, you can view the source of the com_content override, find the token related to google+ and inject inside you own overrides.