Terrain Mesh

HI! I have a question: I have Unity 3D (v 4.3.4f1) free and I create a terrain on my project. I textured and modeled it, I added trees, grass... In the Paint Details section I try to add detail mesh to brush them on map, but is don't work. The Meshes does not apply on the map. I import 3D objects from Blender 3D, Maya, Enthernet, and even from Unity assets, but nothing.

What is the solution of the problem? I must have a script or a material? I need to change something on the object? I proceed correctly?

Thanks!