The string for the name is empty and all location points is 0. I doubt that you will find your surfaces like that. Therefore you can remove the code you marked in red.
So, you have to give the method either the name (id) of the faces you select or the locations.
Study the Remarks section in the Solidworks API reference for further details.
To offset surface you have to use InsertOffsetSurface
See this post for example.
The forum might be able to help further if you explain the process you are trying to do.
The example in your post does exactly what I require.