As soon as you mark an order as shipped (see Create Shipment) you can also add a tracking number and a carrier to the order.
By default Miva Merchant provides tracking links for FedEx, UPS, and USPS. When you mark the item as shipped, your customer will receive an automated email with the tracking number. The tracking number is a hyperlink that the customer can click on and go to the tracking page at the carrier's website.
2.1. In the Type box, enter the carrier's name.
2.2. In the URL box, enter the URL to the carrier's tracking page (with all of the carrier's required parameters) and use the token %tracknum% in place of an actual tracking number. You can get this URL from the carrier.