To post to plugin-enabled sites like this, for the sites, choose “Other”, not “WordPress”, in the Blog field. User name would your WordPress.com account username. Password would be the application password created with these steps: https://wordpress.com/support/third-party-applications/#sites-with-plugins-installed
Hello World!
Welcome to WordPress! This is your first post. Edit or delete it to take the first step in your blogging journey.