when i render, my render screen is black 
There are several possible causes for this, and the easiest way to tell which one it is in your case is to click the “Schematic” button in the bottom left corner of the Main Controls and check for RED nodes in the flow.
If you roll over a red node with the mouse, it will explain at the bottom what the problem is. The typical problem with black rendering is that no lights were created. Krakatoa does NOT use default lights, so you either need a Spot light, an Omni light or some form of Emission enabled. The simplest way to create a light is to right-click the Lighting node in the Schematic Flow and select “Create Default Spotlight”.
As I said, the Schematic Flow shows that you have no lights.
Right-click the node labeled “Sort for 0 Lights” and select “Create Default Spotlight”, or simply create a light manually.
thank u very much…you help me…i love u