This is all you need to post a status to Twitter from a single account. You should also add some error handling.
<?php
require_once('twitteroauth/twitteroauth.php');
/* Create a TwitterOauth object with consumer/user tokens. */
$connection = new TwitterOAuth(‘CONSUMER_KEY’, ‘CONSUMER_SECRET’, ‘ACCESS_TOKEN’, ‘ACCESS_TOKEN_SECRET’);
$connection->post(‘statuses/update’, array(‘status’ => ‘text to tweet’));