Allow Content Author to Publish, But Not Edit or Delete

I would create a new user role, and then assign that role to the user when you create their account. In your functions.php:

add_role('content_writer', 'Content Writer', array(
    'read' => true,
    'publish_posts' => true,
    'edit_posts' => false,
    'delete_posts' => false,
));

You can see the codex for an additional listing of available roles and capabilities.