Open Blender, In edit select preferences, In preferences go to file path option, then in asset Library hit the plus icon button, this will open new File path, select the folder where you saved the "Blender Procedural Realistic Materials" Blender file. Save the preferences. Open Asset Browser editor and here are all your materials.

Open 3D Viewport and Asset Browser Editors side by side, then by just drag & drop these materials on your objects.

These Procedural Materials work best with Cycles render engine, because some of them are using displacement. You can also use Eevee, but my recommendation is Cycles.

You just open Shader editor, where you find a custom node of selected material, from where you can change many parameters according to your requirements. If you don't find custom node in Shader editor just press "Home" button on your keyboard to see the custom node in front of you.