hello im begining use vue, and my project consist in a road crossing a mountain. the road material should be rock, like in cinema 4d my ideia was select the area that should be rock and apply the material. but i dont figure out a way to select those polygons.

Vue isn't a modeller. You cannot select polygons, vertices nor faces. You have several ways of doing this:

One is to create a greyscale map to define where the road and the terrain materials should be applied, and use this map to drive a Mixed material distribution.

Or you can paint your materials directly on the terrain inside the terrain editor.

I suggest you read the manual, there is a tutorial on how to paint materials.

extending onto what bruno said, you can also export a Wavefront .obj file (I find them easiest and the most well behaved) and create materials zones in an external modeler or mapping program, then just import it back in.