[php] Insert data through ajax into mysql database

The ajax is going to be a javascript snippet that passes information to a small php file that does what you want. So in your page, instead of all that php, you want a little javascript, preferable jquery:

function fun()
{
    $.get('\addEmail.php', {email : $(this).val()}, function(data) {
        //here you would write the "you ve been successfully subscribed" div
    });
}

also you input would have to be:

<input type="button" value="subscribe" class="submit" onclick="fun();" />

last the file addEmail.php should look something like:

mysql_connect("localhost","root","");
mysql_select_db("eciticket_db");

error_reporting(E_ALL && ~E_NOTICE);

$email=mysql_real_escape_string($_GET['email']);
$sql="INSERT INTO newsletter_email(email) VALUES ('$email')";
$result=mysql_query($sql);
if($result){
echo "You have been successfully subscribed.";
}
 if(!$sql)
die(mysql_error());

mysql_close();

Also sergey is right, you should use mysqli. That's not everything, but enough to get you started.