Nvivo allows you to import classifications for your files and cases so that you can assign desired attributes at once instead of manually creating them.
In an ideal scenario, you would have your files completed and ready for the import process.
Let's say you completed and transcribed all interviews and created an excel file for your classifications.
You can first import your files and create cases, then import classifications to assign attribute values at ones to those existing files/cases.
However, it is also common that you might need perform additional interviews at a later time and you will be able to import them upon completion. Furthermore, you might want to add or update additional attributes for your data.
In both scenarios you can utilize import classification feature to create/add/update attributes for your files and cases.
In this vide I explained how to do this in both scenarios.
One thing that is critical to this process is you need to prepare your classification as described here so that Nvivo can match existing data with the classification sheet.
I hope this will be helpful.