I creating a path and then applying '3d extrusion from selected path'. but its not extruding to shape, its carving that shape in a box. Why???http://https://www.screencast.com/t/q9hmHDlqjqD9
The problem is with your path not the extrusion.
Set the path operation in the options bar to "Combine shapes" like this :
So you get a path like this :
Yours is currently likely to be set to "Subtract front shape", which is inverting your path:
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