Fatal error: Cannot use try without catch or finally in /users/xxx/www/index.php on line 20

The error means that you code is missing a catch(){} block.

The syntax of try-catch is:

try
{
    //Do something here which might cause an exception
}
catch(Exception $e)
{
   //You are here means that the exception occurred now do something else here.
}

You can also have a finally clause which if always executed whether an exception occurred or not syntax below:

try
{ 
  print "this is our try block\n";
  throw new Exception();
}
catch (Exception $e)
{
  print "something went wrong\n";
}
finally
{
  print "This part is always executed\n";
}

You need to put a catch statement after you close the try block, like this:

<?php
if (!isset($_GET['page'])) {
    header('Location: /main');
    exit();
}

ini_set('display_errors', 'Off');
try {
    $database_host = "localhost";
    $database_name = "NAME";
    $database_user = "USER"; //name for phpMyAdmin in bplaced
    $database_pass = "*******"; //password in phpMyAdmin in bplaced
    global $db;
    $db = mysqli_connect($database_host, $database_user, $database_pass, $database_name) or die('Connect Error (' . mysqli_connect_errno() . ') ' . mysqli_connect_error());
    mysqli_set_charset($db, "utf8");
}
catch (Exception $e) {
    // do something
}

if (isset($_COOKIE['hash'])) {
    $sql = $db->query("SELECT * FROM `users` WHERE `hash` = " . $db->quote($_COOKIE['hash']));
    if ($sql->rowCount() != 0) {
        $row  = $sql->fetch();
        $user = $row;
    }
} 

You are missing the catch block after the try block. Each try must have at least one corresponding catch or finally block in PHP. refer : http://php.net/manual/en/language.exceptions.php