Experiment. That's how I've figured out some machines. Be aware that the bobbin thread is supposed to go in a specific direction; one thing you might not think to try is turning the bobbin over so the thread comes off from the opposite direction.
Also, if you can post specifically what goes wrong when you thread it, we may be able to help. If it doesn't form a stitch at all, sometimes that means that the timing is off and needs to be adjusted by a technician; the problem may not be the threading.