Changed the root directory in nginx. Why can't I access the site?

Question

Nginx

Changed ngnix root directory from /usr/share/nginx/html to /var/www. Now, when trying to access any page of the site, the following error weighs:
What to do with it?

Answer 1

You messed up something in the config, and nginx just won't start. The logs show an error.

Answer 2

Your nginx did not start, see /var/log/nginx/error.log