How to Append materials

Here's a step-by-step process to append a material

Step 1 :  In the main menu at the top of the Blender window, click on "File."

Step 2 : From the drop-down menu, select "Append" or alternatively, use the shortcut Shift + F1.

Step 3 : A file browser window will appear, Navigate to the downloaded .blend file and open it by double clicking or select the blend file and click the append button.

Step 4 : After opening the file, locate and click on the "Materials" folder in the file browser window.

Step 5 : Now select the materials and click Append Button

Now you can assign the material from Material Property tab

How to add materials to library

Here's a step-by-step process to add material to library 

Step 1 : Extract the downloaded zip to a location where you want the shader library

(*Note : you can use the blend file but the zip file contain custom thumbnail images and catalog file)  

Step 2 : In the main menu at the top of the Blender window, click on "Edit."

Step 2 : From the drop-down menu, select "Preference" 

Step 3 : Blender Preference window will appear. in that window select 'File Path'

Step 4 : Scroll down to Asset libraries tab and click on the '+' button

Step 5 : A file browser window will appear, Navigate into the extracted '3d_monkeyx Procedural Shaders Vol-01' folder

Double click to open the folder

Step 6 : Now click 'Add Asset Library" button 

Now the shaders  will added the asset Library

Step 6 : In asset browser , click the asset list menu and select 3d_monkeyx Procedural Shader Vol-01 or All

Now you can drag and drop material to object and customize the material in node editor or Material property tab