PFCEx is a command line tool, so you need to run it from a Command Prompt.
Usually a Prompt is launched form Start -> Accessories -> Command Prompt.
As an alternative, you could do: Start -> Run..., type CMD and press enter.
When the command prompt is opened, you need to change the current
directory to where you installed PFCEx. For example:
c:\Documents and Settings\John> cd \pfcex
then you can run PFCEx against a PFC file of your choice, specifying
his full pathname, as in:
c:\pfcex> pfcex \myfolder\myaolfile.pfc
The output will be shown on video, and a pfcex.html file will be
created in the current folder. You can then open it with your browser.