Choose "Pack" if you want your Shipment to be packed so you can see the final weight in your account and decide on the shipping method (the Shipment will have status 'Packed').

Choose "Pack and Ship" to get your Shipment packed and ready to go. In other words, instead of returning to the warehouse, your Shipment will receive the 'Ready for shipping' status and will be sent out in the next batch, saving you up to 24 hours.

However, with "Pack and Ship" option you cannot change the delivery address, shipping method, and you also need to have sufficient funds on your balance for the Shipment to be sent out straight away. If your account balance is too low, your Shipment will be returned to the warehouse with the status "Payment Required".