First of all: PHP's $_GET is not a method. As you can see in the documentation $_GET is simply an array initialized with the GET's parameters your web server received during the current query. As such it is not what you want to use for this kind of things.
What you should look into is cURL that allows you to compose even fairly complex query, send to the destination server and retrieve the response. For example for a POST request you could do something like:
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,"http://www.mysite.com/tester.phtml");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS,
"postvar1=value1&postvar2=value2&postvar3=value3");
// in real life you should use something like:
// curl_setopt($ch, CURLOPT_POSTFIELDS,
// http_build_query(array('postvar1' => 'value1')));
// receive server response ...
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$server_output = curl_exec ($ch);
curl_close ($ch);
Of course if you don't have to do any complex query but simple GET requests you can go with the PHP function file_get_contents
After you received the web page content you have to parse it. IMHO the best way to do this is by using PHP's DOM functions. How to use them should really be another question, but you can find tons of example without much effort.