User_nicename vs nickname

I have updated Nickname for user. It’s saved in usermeta table. There is no way to change user_nicename. I tried to use nicname from the_author_meta(“nickname”). But author url does not work from nickname. It works good with user_nicename.

1. What’s the purpose of nickname then?
2. Why do you need to have user_nicename and nickname?
3. How to change user_nicename from user profile.