ช่วยอธิบายโค้ดนี้ให้หน่อยนะครับ ว่าตัวไหนทำงานอะไร

$check_date = "";

foreach($_POST["date1"] as $key=>$val){
  $stime = $_POST["hour1"][$key].':'. $_POST["min1"][$key];
    $etime = $_POST["hour2"][$key].':'. $_POST["min2"][$key];
	$room=$_POST['txtroom'];

	$strSQL = "SELECT * FROM booking WHERE r_id = '".$room."' 
AND ((sdate='".$val."')) AND (('".$stime."' BETWEEN stime  AND etime) OR ('".$etime."' BETWEEN  stime  AND etime )OR (stime between '".$stime."' and '".$etime."') OR (etime between '".$stime."' and '".$etime."'))";
	$objQuery = mysql_query($strSQL) or die(mysql_error());
	$objResult = mysql_fetch_array($objQuery);

	    

if($objResult['sdate']){
	  	     $check_date.= $objResult['sdate']. ' เวลา '. $stime .' - '. $etime;
}
}
	if($check_date != "")
{

		echo "<script>alert('ห้องนี้วันที่ $check_date มีผู้ใช้งานแล้ว');history.back();</script>";
}			 
			 
		else{ 
				
	$m_id=$_POST['txtm_id'];
	$name=$_POST['txtname'];
	$sex=$_POST['txtsex'];
	$org=$_POST['txtorg'];
	$tel=$_POST['txttel'];
	$fax=$_POST['txtfax'];
	$mail=$_POST['txtmail'];
	$sql="INSERT INTO `bkkbooking`.`member` (`name` ,`sex` ,`organ` ,`tel` ,`fax` ,`email` ,`type` )
VALUES ('".$name."', '".$sex."', '".$org."', '".$tel."', '".$fax."', '".$mail."', '0')";
$result = mysql_query($sql) or die(mysql_error());
$id=mysql_insert_id();
if($sql){

foreach($_POST["date1"] as $key=>$val){
    $startTime = $_POST["hour1"][$key].':'. $_POST["min1"][$key];
    $stopTime = $_POST["hour2"][$key].':'. $_POST["min2"][$key];

	$room=$_POST["txtroom"];
	$detail=$_POST["txtdetail"];
$sql_insert = " INSERT INTO `bkkbooking`.`booking` (`m_id` ,`appdate` ,`sdate` ,`edate` ,`stime` ,`etime` ,`r_id` ,`detail` ,`status` )";
$sql_insert.= " VALUES('".$id."','".date("Y-m-d")."','".$val."','".$val."', '".$startTime."','".$stopTime."','".$room."','".$detail."','0'); ";
$objQuery = mysql_query($sql_insert) or die(mysql_error());

}