You can archive shipments in 3 ways:
1. Wait 24 hours, assuming the shipment is complete, after 24 hours the shipment will automatically be archived, to help keep things organised.
2. Select the 'archive' option from the dropdown menu at the end of each shipment row in the shipments list
Note : You can still search for archived shipments just like you can with non archived shipments
You can read all the statuses here