This extension comes at the moment without any UI. Compared to plugins, like the SolidWorks plugins, this one only executes a command in the background to get your file automatically converted. At the moment only FreeCADs file format is supported, but I’m planning to allow also file formats, which are also supported by FreeCAD.
Recommendation for Ubuntu users:
Please enable and use the FreeCAD stable PPA. There are issues in the official packaging by Canonical. I can highly recommend following the instructions in the FreeCAD wiki, which explain how to set up the PPA either graphically or via console.