Once selected, V-Ray will automatically scan the folder. You may need to click or restart your 3D software.
For official documentation and troubleshooting, you can visit the Chaos Docs V-Ray Material Library page . V-Ray Material Library - V-Ray for Rhino - Chaos Docs vray 6 material library link
Inside your 3D application (e.g., 3ds Max or SketchUp), open the V-Ray toolbar. Once selected, V-Ray will automatically scan the folder
C:\Users\%USERNAME%\Documents\V-Ray Material Library 3ds Max or SketchUp)
To help find the exact steps for your specific setup, tell me: