Thanks for answer!
No, i mean not this.
I set up new posts to look like “domain.com/%postname%.html”
it’s fine.
New pages, tags and categories by default, its ok too.
I would like to make few new pages their address to look like “domain.com/free/lesson 1”, “…/free/lesson2”, “…/free/lesson3”
How to add prefix “/free/” to these particular pages only?