Understanding what your reference number is with your shipping company and why it is so important could actually go a surprisingly long way to making your relationship with your courier services run that much more smoothly. This number is what you will receive from the courier once you place an order with them. They will likely give it to you over the phone or by email if that is how you previously placed your order, but you will also see it on every piece of correspondence, including receipts and invoices, that you exchange with the courier company.
When shipping, the first thing that you want to have in your relevant files about any shipments with a courier is the reference number that they give you, because this is the most important piece of information you have when it comes to accessing your information about this shipment with the courier. Every bit of information that they have regarding your shipment is going to be tied to that number, so always having it to hand means that you will be able to receive much better service from your delivery company.
Some people who are long term account holders with a courier will assume that they will always have their information stored in an account and won't worry too much about keeping a hold of their reference number, which is a mistake. Because the reference number is tied to the individual shipment, it will always be accurate regarding that shipment. However, simple human error could cause that information to be attached to the wrong account in the courier's records, which is why if you ever had a dispute about the shipment it would be much more important for you to have the reference number than simply to provide them with your account information.
Finally, checking the status of a shipment is something that most people who ship with a courier company on any sort of a regular basis like to do. Your reference number is how you can check on the status of your shipment. All you will have to do is either provide it to someone over the phone or enter it in the website for your courier company. You will then be either told the last major point that your status went through or be provided with its real time location via GPS tracking, as well as receiving any other pertinent information such as if the shipment has been slowed down.