Error while installing theme

Directories: 755
Files: 644
Ownership should match the ID of the ID under which the PHP process is running.

I will correct the permissions. I installed it as root and the group and owner are root. I saw the group and owner of the .htaccess file to be www-data. I assume that this is the web server itself. I will change all group and owner to www-data.

Oh, my. NEVER EVER run your web server as root! In fact, while the Debian/Ubuntu systems default to www-data, it’s best to create a specific user for each site you host on the server, for both the files and the PHP process.

I read the detailed documentation but it didn’t specify who should be installing it. Whose ID should I install it under?

When I set up a site, I create a new user (e.g., “www-sterndata” and give ownership of /var/www/sterndata (and below) to that user. In my php-fpm config for this virtual host, I set it to run as “www-sterndata”, too.

How? For the mechanics within your distro, check with its support community.

This is not part of the WP install itself, but the configuration you need to do to set up a WP hosting environment.