Why are you looking for the
/var/www/ directory (Apache's default root directory)? According to the article you cited, you're supposed to use Nginx (and not Apache).
"Is there a sites/all folder, or something equivalent?"
According to Step 3 of that same article, you were to (manually) create a new directory in which to store your drupal files. Did you do that?
"Will change to Nginx+Apache configuration."
Why would you want to do that?
"... but still couldn't find it."
Could not find, what?