You must launch "Mission_editor.jar" file. But I recommend you to check first HarryH's very well written tutorial (link is on previous pages)and than start fiddling with editor. Also, I am going to relase clean WOFF UE Mission editor version without the current WOFF3 hook, because if you run editor and do not open any mission file, your WOFF "simulation.xml" file is renamed to "simulation.xml.editor.bak" and WOFF will crash.