Ok, i apoligize for my mistake.
I should make only Lesson pages appear in the footer, a button that I need to do some action.
I have intervened in the general.php file of the theme that I use clearly so doing the button appears in the footer of all the moodle pages. I want it to appear only in the pages that are showing the lessons. It's possible? In which part of the code do I have to intervene to do this? What is the distinction that makes Moodle understand that I am finding myself on a page that shows me a lesson? Thank you