I am trying to get Drupal 8 installed on Ubuntu 18.04. I have installed LAMP and composer. I will install Drupal 8 with this (I think this is the latest recommended way) ...

composer create-project drupal/recommended-project my_site_name_dir

Where should my_site_name_dir be?

Some guides suggest it should be at apache2's web directory: /var/www/html/my_site_name_dir. And then change the directory owner to www-data (for apaches benefit?). But how then does Composer or myself write files to this directory if the owner is changed?

This guide Using Composer to Install Drupal says:

Your 'my_site_name_dir' will contain files that should be outside of your web root and not accessible by the web server. The web root will be 'my_site_name_dir/web'

So am I right in thinking that my_site_name_dir should not be visible by apache, but my_site_name_dir/web should be? If so how to I tell apache to find it?

I was imaging that my_site_name_dir would be somewhere in my home directory (easier for dealing with file permissions?) and I would view it in a browser with something like: http://localhost/my_site_name_dir

(I'm struggling a bit trying to grasp file ownership and how composer works.)