I only have order number.. is that useful to track?
Nope, you need the tracking number. Also, if you have only the order number, then that means your order has not been shipped yet. You will be getting one more email from them after they have shipped which will have your tracking number. This email will have a shipping and handling fee(at least did for me). The very first email I received from them about order confirmation said $0.00 for subtotal too.