you cannot simply copy paste stuff in this folder using your file browser, It is protected for security reasons, you will get a permission denied error message because by default you don't have write access permission here.
Follow these Steps:
execute these commands to set all permissions for /var/www directory
sudo adduser <username> www-data sudo chown -R www-data:www-data /var/www sudo chmod -R g+rwX /var/www
Now you can copy, edit and create files in /var/www folder just like any other folder.