Here follows a short summary of how to append the materials into your own scenes:
- Open your scene.
- Go to File > Append (or Link).
- Navigate to the Granites.blend file.
- Click on the blend file to view its contents.
- Navigate to the NodeTree folder and select the Granite_... node groups to load the shaders.
For the complete documentation on linking and appending, view the Blender documentation: Blender Appending And Linking.