First, create a plane at the desired dimensions. This will be your carpet. With the plane selected, go to ???Create > Vray > Vray Fur??? By default, the vray fur will be linked to your plane. Assign them a desired material (keeping both the plane and the vray fur gizmo selected) and leave all the rest of the parameters unchanged for the moment. If you hit a test rendering at this point you should end up with something like the following: