Google Cloud API Integration in PHP

I need a php page that I can use as a reference to integrate into our software of using Google API 2.15.3 to be able to upload, download & delete files from Google Cloud using a service account (no end user authentication). I don't need a user interface to be able to list out the files or upload them but just need this as a reference. It should be very simple and straightforward using these variables or something like this.

<?php
require_once '/home/public_html/googleapi/vendor/autoload.php';

$strKeyFile = "/home/public_html/googleapi/key/server-jfdkl32ldfjkl.p12";
$strLocalStorageFolder = "/home/public_html/files/";
$strFile = "filename.jpg";
$strGoogleProjectID = "myproject";
$strGoogleBucker = "uploads";