Once the button is pressed, look for the .sut file that you would like to convert (make sure there are no '.'s in the name as that will cause a few minor errors right now ). Once selected, a .png file ...

A folder "the_addon_name" --> containing always (and at least) an "__init__.py" file. The folder of a multifile addon is nearly always downloaded zipped. Go to preferences, addons, click on "install..