lil' db class

db.php

<?php
class DB {
public static function connectDb()
    { 
        $host = 'localhost';
        $dbname = 'hhahh';
        $user = 'hhahh';
        $password = 'hhahh';

        $db = new PDO("mysql:host=$host;dbname=$dbname", $user, $password);
        
    }

public static function check() {
    $st = $db->prepare("SELECT `password` FROM `users` WHERE `login` = :login AND `password` = :password");
    $st->bindValue(":login", $login, PDO::PARAM_STR);
    $st->bindValue(":password", $password, PDO::PARAM_STR);
    $st->execute();
    $db = null;
}
public static function insert() {
    $st = $db->prepare("INSERT INTO `users` (`login`, `password`) VALUES(:login, :password)");
    $st->bindValue(":login", $login, PDO::PARAM_STR);
    $st->bindValue(":password", $password, PDO::PARAM_STR);
    $st->execute();
    $db = null;
}
}
?>

Find bugs and tell me!