php初学有一段代码看不懂，请教.

文件index.php 源码内容：
<?php
if(!file_exists(dirname(__FILE__) . "/data/common.inc.php"))  ---(__FILE__) 啥意思？
{
    header("Location:install/index.php"); ---这句啥意思？
{                     
    exit();
}
require_once (dirname(__FILE__) . "/include/common.inc.php");
require_once DEDEINC."/arc.partview.class.php";
$GLOBALS['_arclistEnv'] = 'index';
$row = $dsql->GetOne("Select * from `#@__homepageset`");
$row['templet'] = MfTemplet($row['templet']);
$pv = new PartView();
$pv->SetTemplet($cfg_basedir . $cfg_templets_dir . "/" . $row['templet']);  ---这句啥意思？“->”是啥磨？
$pv->Display();

?>

---

PHP code:

if(!file_exists(dirname(__FILE__) . "/data/common.inc.php")) //(__FILE__) 魔术变量，dirname(__FILE__)定义根目录？
{
header("Location:install/index.php"); //面页跳转
{
exit();
}
require_once (dirname(__FILE__) . "/include/common.inc.php");
require_once DEDEINC."/arc.partview.class.php";
$GLOBALS['_arclistEnv'] = 'index';
$row = $dsql->GetOne("