Sort data by newest to oldest PHP

I have data stored on a database and I'm showing it on a webpage, at the moment it's ordering it from oldest to newest but I would like the newest to be shown first, I have tried a few things like adding this code that i found on another stack overflow question;

$files[$mod_time] = $basedir.'/'.$filename;

and tried doing a mysql query like this;

$query = mysql_query("SELECT * FROM users LIMIT $start, $per_page ORDER BY ID DESC");

maybe I'm not putting the code in the right place, here is the section of my code that's pulling the data;

if ( $stmt = $mysqli->prepare("SELECT * FROM memo Where uid = ? " ) ) {
    $stmt->bind_param("i", $uid2);
    $stmt -> execute();
    $stmt -> bind_result($id, $note, $uid3);
 }
        $output=array();
        $out_id=array();
        $out_note=array();
        $i=0;
            while ($stmt->fetch()) {
                //$out_id[$i]=$id;
                //echo $out_id[$i] . " / ";
                $out_note[$i]=$note;
               echo $out_note[$i]. " <br>";
               //echo $i. "<br>";
                $i++;    
            }
        $output = array($out_note,$out_id);
        rsort($output);

I'm new to PHP, any help or advice would be good for me, thanks a lot.