I have no clue what I m doing

programming
1 
<?php
$_GET["un"];
$_GET["pw"];
$_GET["pwverify"];
$_GET["mail"];
$pw=($_POST["pw"]);
$pwverify=($_POST["pwverify"]);
$mail=($_POST["mail"]);
$un=($_POST["un"]);
if ($pw==$pwverify) {
   echo("ACCSESS OK")
   }else{
    echo('<SCRIPT language="JavaScript">
window.location="window.register.php?error=P";
</SCRIPT>');
}
if ($un=="" or $pw=="" or $pwverify=="" or $mail=="") {
    echo('<SCRIPT language="JavaScript">
window.location="window.register.php?error=U";
</SCRIPT>')
 }else{   
echo("ACCESS OK");
}
mysql_connect("localhost", "babolo", "")
   or die("Could not connect: " . mysql_error());
echo "Connected successfully";
mysql_select_db("babolo") or die ("couldnt connect to database");
mysql_insert_id($un) or die ("couldn't insert variable");
mysql_insert_id($mail) or die ("couldn't insert variable");
mysql_insert_id($pw) or die ("couldn't insert variable");
mysql_insert_id($pwverify) or die ("couldn't insert variable");
?>

Could someone please help me with this code I want these variables sent to database table called users on the db babolo