I recently wanted to perform a HEAD request to a file, after which I wanted to perform some more advanced HTTP interaction, so CURL was also the tool of choice here.

He started with the (slow?) command line to get the parameters right before moving into PHP. After picking out the right ones ("curl -I -X HEAD http://localhost/admin/") he transfers them into a series of curl_setopt calls that specifies a HEAD request type and no content to send (with CURLOPT_NOBODY).