How to fracture/destroy in unity.

It's extraordinarily difficult to take an arbitrary mesh and "shatter" it completely procedurally. The way this is usually done is to build the mesh in "parts" (the broken pieces), and assemble them in the game so that they appear whole. When that is done, they will appear just as they would if they were one single mesh. The next step is to add a destruction script. This is actually fairly easy. You can either attach a Rigidbody to each of these objects, and disable it until the mesh is destroyed, or add a Rigidbody to each piece when it is destroyed. Then, applying a random force to each Rigidbody, you can have it "explode" outward, each piece going off in a different direction.