This file you sent is one of the files that compose a Chimera extension named SSE Tracer.  The file you sent indicates that there must be at least one additional file (named gui.py) and there may be others.  So, the ChimeraExtension.py file and the gui.py and whatever other files should all be together in one folder, let’s call it "sse-tracer" for example purposes.  You would get Chimera to load the extension by choosing Chimera’s Favorites->Add to Favorites/Toolbar… menu entry.  At the bottom of the resulting dialog is a “Locations” box that is probably empty in your case.  Use the “Add…” button below the box and in the resulting dialog choose the folder containing the sse-tracer folder (not the sse-tracer folder itself!) — i.e. the parent folder for sse-tracer.  Click OK on the file dialog and the SSE Tracer extension should appear in Chimera’s Tools->Utilities menu.  You probably also want to click “Save” on the Tools preferences dialog you were using so that Chimera will remember where to look for the SSE Tracer extension the next time you use Chimera.

Now, I have no idea how the SSE Tracer extension itself works — I didn’t know it existed until you sent your mail.  Hopefully, there was some documentation for it that came along with your download.

—Eric