The packing process starts after both the buyer and the supplier have signed and finalized an agreement. As a supplier, it is your responsibility to deliver the items to the buyer, as per the conditions mentioned in the final agreement. Before starting the actual delivery, you should plan how to deliver the required items in an optimal manner. For that, you create preliminary packing lists (PPL) and preliminary packages, which are estimates for the actual delivery. After you create the PPLs, you submit them for approval from the buyer.
Have a look at the whole packing process through the below video:
The buyer sends you the release notes, which may or may not match exactly with the PPLs you sent. The release notes contain specific delivery details (like the delivery location, delivery date, and so on) for a group of item shipments. After receiving the release notes, you create packages and assign the line items to the packages. After all the items in a release note are assigned to packages, you must submit the packages' details for the approval from the buyer. After the buyer approves the packages, you can start the process for actual delivery of the packages.
The Packing tab is visible only if packing information is available. That happens when the buyer invites a supplier to start preliminary packing or approves a release note.