As a follow up, I perused the help file and guess what, not too helpful.  The following tutorial fro ShareCG.com will make the process clearer:

http://www.sharecg.com/v/36268/PDF-Tutorial/Injection-Pose-Builder---The-Easy-Way?PSID=9bbe8f393eaa19274673e23d826cbd23

The Link Library is a compiled library storing the figure morph information from which you are creating your custom character.  It is a reference point for constructing your INJ/REM files.