Hello,
maybe my question is easy, but I don't know: how to add text to each course. Where add to template course?
That is simply the text added to Topic 0 when the editing is turned on (as you can see if you go back to the School demo site school.demo.moodle.net logging in with username teacher and password moodle and clicking the pencil icon. Are you wanting to have all your courses with the same heading in the top section? You could explore using course templates - see Adding a new course