VMPPmax User Library manager can operate only with one “global” material library partitioned into Sections and Categories (Folders and libraries).
The “global” user material library can be by default in C:\VMPPmax\userlib or in any other place. The path to library can be set in VMPPmax settings “User Directory Location“.

Keyboard Shortcuts:
F2 = Rename
Shift+M = Assign Material to Material Editor Active slot
Shift+O = Assign Material to selected Object(s)
Alt+M = Get Material from Material Editor Active slot
Alt+O = Get Material from selected Object
NumPad1 = Render Single Thumbnail Draft
NumPad2 = Render Single Thumbnail Medium
NumPad3 = Render Single Thumbnail Best
NumPad4 = Render Category Thumbnails Draft
NumPad5 = Render Category Thumbnails Medium
NumPad6 = Render Category Thumbnails Best
Alt+N = Add/Edit Comment
User Library rename Dialog
Escape = Cancel and Close
Enter or F2 = Accept changes and Close
Short video how to use Material Manager.