Once an order is shipped by your supplier, he will add the tracking number to the shipping information. You can get this tracking number by going to your “Orders” section.
The supplier will also add the carrier name. From there, just look for the tracking software of the carrier on the internet. You can use Parcelapp, which supports a lot of carriers for your tracking.
If your order is connected to Shopify, the tracking information will be automatically sent to the corresponding Shopify order.
So your customer will be automatically notified with the tracking number once the order is sent.