NETVAULT-how to determine the use of a library or standalone device.

I've got the pleasure of assuming backup admin position on a system
and technology I know nada about. We're using Netvault Version 7.10
Build 42. My experience in the past was with doing backups to tape,
up until two weeks ago I have never even heard of a VDL. So my
questions are these these: how do I go about deciding if I want to use
a standalone device or a library? and where is a good place to go to
learn more about VDLs?

thx
phil