Use
The
pack option gives you the option of packing material, handling units, or delivery items.Non-assigned handling units: It is possible to create handling units without reference to a document. Assign the material items and the packaging material to this handling unit. The packed material is posted to a storage location. The handling units created here are handling units with inventory management information. If the storage location is warehouse-managed, stock information will also be created.
Handling units assigned to a delivery: Packing is part of delivery and shipment processing. During delivery processing, you can select the delivery items that you would like to pack and assign them to handling units. If the incoming goods are stored in a handling unit-managed storage location, it is mandatory to pack them.

In Customizing for Handling Unit Management you can create packaging material for a warehouse. Choose Basics ® Warehouse Management ® Define Control for Automatic Creation of Pick HUs.
This material will be displayed automatically upon packing goods. You can also override it with a different packaging material.
The
unpack option enables you to unpack handling units that are already packed. This can be necessary if you want to adjust a quantity of the packed material, for example.