We have previously referred you to NBU documentation.
All of these topics are well covered in NBU Admin Guide I - the 'basics', the 'why', the 'how', etc.
NBU Admin Guide for Windows, Volume I http://www.symantec.com/docs/DOC3653
Please take your time and read though the relevant sections. Ask questions if there is something specific that you do not understand and cannot figure out by comparing the theory in the manuals with your environment.
Links to all manuals for the different NBU versions can be found in 'Handy NBU Links' in my signature.
*** EDIT ***
Just have a look at the topics covered in Chapter 9 of Admin Guide I (link above):
Inventorying robots
This chapter includes the following topics:
■ About robot inventory
■ When to inventory a robot
■ About showing a robot's contents
■ Showing the media in a robot
■ About comparing a robot's contents with the volume configuration
■ Comparing media in a robot with the volume configuration
■ About updating the volume configuration
■ Updating the volume configuration with a robot's contents
■ Robot inventory options
■ Configuring media settings
■ About bar codes
■ Configuring bar code rules
■ Configuring media ID generation rules
■ Configuring media type mappings
■ About the vmphyinv physical inventory utility
■ Example volume configuration updates
