This addon is a plugin. You need to extract it to your /plugins folder to install it.
It already contains the newest (minified) version of SHJS.
Just add class="LANG" to code tag, e.g. php, python, sql.
Changelog: 1.1 (2011-01-12): - default language when no "class" attribute is set - option for disable js auto-update (usefull with ajax editing)