To help you find specific materials you have different options.
You can go through the different material categories, click the preview thumbnail and browse all the materials in that category.
Material icons will help you identify different aspects of each material
Filters will make it easier to find specific materials.
You can filter by Render Engine, Complexity, UV’s required, Use Displacement or any combination of them.
The materials that don’t match your criteria, will not be listed in the categories.
There’s an option in the addon preferences to show or hide filters.
On the top right corner of the material preview, you will find a search icon:
This will allow you to search through categories and material names (I will probably add tags in the future). After you enter the search string you need to hit enter on the keyboard to search.
The materials that match your search will be listed and you can click their name to select them.