In World Editor I found an option Grass Range. But I can't find how to paint grass.. Anyone can help me?

In Object Mode: Object->Object Brush. You'll see a window where you can put your grass objects (and optionally save to txt file list of these objects). Then you can put your grass on the world by pushing RMB and LMB.

Thanks..

You can also do that with any object it doesn't have to be just grass