<?php
session_start();
mysql_connect("host", "user", "pass") or die(mysql_error());
mysql_select_db("db_name") or die(mysql_error());

$creator = $_SESSION['username'];
$message = $_POST['message'];
$time = time();

$q="INSERT INTO chat (`creator`,`message`, `time`) VALUES ('$creator','$message', '$time')";
mysql_query($q);
?>