As a CGI program, this should be invoked through your web server. If you run it from the command line, it will either complain about unauthorized access or spew a bunch of HTML at you.
upsstats.cgi uses template files to build web pages containing status information from UPS hardware. It can repeat sections of those template files to monitor several UPSes simultaneously, or focus on a single UPS.
These templates can also include references to upsimage.cgi(8) for graphical displays of battery charge levels, voltage readings, and the UPS load.
The web page that is displayed is actually a template containing commands to upsstats which are replaced by status information. The default file used for the overview is upsstats.html.
When monitoring a single UPS, the file displayed is upsstats-single.html.
The format of these files, including the possible commands, is documented in upsstats.html(5).
The NUT (Network UPS Tools) home page: http://www.networkupstools.org/