I'm not sure I get your problem right. I guess, though:)
Simply loading textures via the Library Manager won't make them available as materials. They will be available to be selected when defining materials.
In this case I can imagine two different scenarios. Normally, you have to create your own materials based on the given textures. But libraries and library parts can define materials themselves. You should ask the provider of the library whether it creates materials for itself or you should create them manually.
HTH,
Zsolt Táskai
ArchiCAD Development - GDL Team
AC13, AC14 and upwards...