The filer requires a software license to enable NFS services. The license is installed on the filer at the factory per your order, so the initial setup of your filer does not involve entering license codes.
You need to enter license codes only if any of the following conditions applies:
You purchased a filer with a release earlier than Data ONTAP 4.0 and you are upgrading it.
You want to enable NFS service, which was not previously licensed for your filer.
You reinstalled the file system on your filer.
Network Appliance provides you with the appropriate license codes when shipping you the software upgrade kit or when giving you instructions for obtaining the software upgrade over the Internet.