The "Manifest" operation applies to certain carriers and service providers. Typically, at the end of your shipping day, before you tender a collection of packages to your service provider, you are required to upload a "manifest" file, and print out a sheet of paper to give the driver.
The Manifest API perform this action given a list of orders. You are expected to provide specific TxnIds or TrackingNumbers that will be included in the manifest. Upon success, Teapplix will return a PDF document that you can print out to be included with the packages: