//Upper first letter in class name
class Db_connect{
    public $db_host = "localhost";
    public $db_user = "katalog";

    //must be DATABASE name, not TABLE name
    public $db_table = "katalog";
    public $db_pass = "parika825";

    public function __construct(){

    //mysql is deprecated driver. use mysqli,pdo,etc.
    mysql_connect($this->db_host, $this->db_user, $this->db_pass) or die("Не могу соединиться с MySQL.");
    mysql_select_db($this->db_table) or die("Не могу подключиться к базе.");
    }
}
$con = new Db_connect();