WHAT else is needed to use UV2UV ?

UV2UV is a stand-alone application.

But in order to completely achieve a texturing project you will also need an application that enables UV mapping manipulations.

You can use your favorite 3D package (Maya, 3DS Max, etc.) or a specific tool like
UV Mapper.

You will also need a 3D application (3D viewer or renderer) in order to look how your new UV2UV texture perfectly suits your object !