Getting started with the Facebook PHP SDK v4.1. Part b: Setting up the application.

fb_php_sdk_4.1b.php

<?php

// setup application using API keys and handlers
$fb = new Facebook\Facebook([
  'app_id' => 'xxx',
  'app_secret' => 'yyy',
  'http_client_handler' => 'curl', // can be changed to stream or guzzle
  'persistent_data_handler' => 'session' // make sure session has started
]);