The package is invoked with 1 option: \usepackage[xxx]{harpoon},
where xxx is your favourite graphics device driver. On most Unix
machines, this will be dvips and on a Macintosh this could be oztex. Refer to the graphics package for more information.
The commands are
\overleftharp, which looks like this
\overrightharp, which looks like this
\overleftharpdown, which looks like this
\overrightharpdown, which looks like this
\underleftharp, which looks like this
\underrightharp, which looks like this
\underleftharpdown, which looks like this
\underrightharpdown, which looks like this