Как правильно пользоваться классами в php?

Разобрался сам, спасибо за подсказки по поводу $this.

<?php
class le {
public function __construct()
{
$this->set  = json_decode(file_get_contents('engine/settings.json'), true);
$this->lang = json_decode(file_get_contents('engine/languages/'.$this->set['ui']['language'].'.json'), true);
$this->tpl  = unserialize(file_get_contents('engine/templates/'.$this->set['ui']['template'].'.serialize'));
$this->db   = new PDO('mysql:host='.$this->set['db']['host'].';dbname='.$this->set['db']['name'].';charset=utf8',$this->set['db']['user'],$this->set['db']['pass']);
}
public function query($sql, $params)
{
    $query = $this->db->prepare($sql);
    $query->execute($params);
    return $query;
}
public function ndate($a)
{
    date_default_timezone_set('Europe/Moscow');
    $ndate = date('d.m.Y', $a);
    $ndate_time = date('H:i', $a);
    $ndate_exp = explode('.', $ndate);
    $nmonth = array(
        1 => 'янв',
        2 => 'фев',
        3 => 'мар',
        4 => 'апр',
        5 => 'мая',
        6 => 'июн',
        7 => 'июл',
        8 => 'авг',
        9 => 'сен',
        10 => 'окт',
        11 => 'ноя',
        12 => 'дек'
    );
    foreach($nmonth as $key => $value)
    if ($key == intval($ndate_exp[1])) $nmonth_name = $value;
    if ($ndate == date('d.m.Y')) return 'сегодня в ' . $ndate_time;
    elseif ($ndate == date('d.m.Y', strtotime('-1 day'))) return 'вчера в ' . $ndate_time;
    else return $ndate_exp[0] . ' ' . $nmonth_name . ' ' . $ndate_exp[2] . ' в ' . $ndate_time;
}
public function views($value)
{
    if ($value >= 1000) return round($value / 1000, 1).'K';
    else return $value;
}
public function json($url)
{
$cURL = curl_init();
curl_setopt($cURL, CURLOPT_URL, $url);
curl_setopt($cURL, CURLOPT_HTTPGET, true);
curl_setopt($cURL, CURLOPT_HTTPHEADER, array(
'Content-Type: application/json',
'Accept: application/json'
));
curl_setopt($cURL, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($cURL);
curl_close($cURL);
return json_decode($result, true);
}
public function cache($function, $content) {
if (is_null($content)) {
$cache = $this->query('SELECT expires FROM cache WHERE function = ?',array($function))->fetch(PDO::FETCH_ASSOC)['expires'];
if (is_null($cache)) {
$this->query('INSERT INTO `cache`(`function`, `expires`) VALUES (?,?)',array($function, time() - $set['int']['cache_time']));
return time() - $set['int']['cache_time'];
}
else return $cache;
}
else if (!is_null($content)) {
file_put_contents('engine/cache/'.$function.'.html', $content);
$this->query('UPDATE `cache` SET `expires`= ? WHERE function = ?',array(time() + $set['int']['cache_time'], $function));
}
}
}
?>