FFD is a plug-in written by Chris Phillips, the same guy who brought you SketchyPhysics.
FFD uses Construction Points (CP's) to be able to manipulate the deformation grid. After each CP or set of CP's has been moved or rotated, the mesh automatically updates and the results are instantly shown (calculations may take some time depending on the Face count if the mesh).

So first a CP control grid is positioned over the mesh, shown above, still a Group in the model. First the Group must be exploded, then made into a Group again. FFD does not recognize the SDS Group as a genuine SketchUp group, hence the extra operation.
With a CP grid of 2 x 2 x 6 SketchUp calculates the CP grid onto the mesh. This process is called 'weighing'.