What is the relationship between authority and mental well-being?

Whether it is harassment or simply affirmation and education, how do we know how to say "No"? At what point should we verbalize the fact that we disagree? And how do we set limits? How can we show authority? For a long time, parents had a relationship of power with their children. Today, this notion has been replaced by authority. But what then is authority, and how does it work?