Hi Zohreh
Which platform are you using (linux, mac, which version)?
Slicer 4.4.0 external modules still seem to have some hickups on the Mac (it should work on linux though). Can you try Slicer 4.3.1? (you can download 4.3.1 here: http://slicer.kitware.com/midas3/slicerpackages/view ).

For usage information, check out the tutorial and the InsightJournal document (though both clearly need updating).

Martin