Two ways to assign materials in V-Ray

1. Click in the V-Ray toolbar on the Material Editor to open it. Create a meterial then in the SketchUp Material
click "in model" .and click the surface to apply the material.

2. Select the "Paint Bucket" and click on the surface  that you want to apply the material.

3. Now the objects are applied with materials. You can open the Material Editor to edit and create other materials.