This document (https://developer.android.com/google/gcm/http.html) describes the Google Cloud Messaging (GCM) HTTP connection server. Connection servers are the Google-provided servers that take messages from the 3rd-party application server and sending them to the device. Consider i prepared a HTTP server for GCM based on this document. how i can send information to GCM with PHP? should i use POST method? how? or it doesn't related to PHP?
Yes, you should send a POST request to https://android.googleapis.com/gcm/send. It doesn't matter which language you are using in your server. PHP would work just fine.