no probs, that a fair question.
By default, blender doesn t come with a built-in material library. like i said, you can download material libraries from any good blender files websites (if you ask for this, we will provide you some usefull links to it).
Most of the artists are making their own matlibs, after creating them. because in most case, you will never use the materials made by someone else 
but to prototype your project, you may be interested to look at “how” people are making it, using nodes and textures.
About the preview system and mat manager… again, if you understand it… a library is usually a blend file, that contains materials… and the few addons that can allow you to visualize them before apply are the ones you have seen…
For blender 2.79 (very good) : [Addon] Blend Library - Asset manager for materials, objects and nodes
For Blender 2.8 : the same one, but it is included into the official release no need to download
this feature allow you to previsualize, load, apply and much more
hope it helps… enjoy