Download TeXcount (version 2.3): script and documentation.
The documentation, included in the download package, explains how TeXcount works, including its strengths and short-comings. It also explains the options and how you can add new macro handling rules.
The script requires Perl. This is standard under Unix/Linux. A Perl version for Windows is ActivePerl.
Download TeXcount version 3.0α (9 Jan 2012) to test the coming version.
With version 3.0 there will be a number of new features:
Overview of older versions (available for download) and change history.