This is a Nagios plugin, so you install it and configure a service check in Nagios and it runs whenever Nagios calls it and reports back on the status of whatever it's monitoring. It takes one parameter (-u) which tells it the Graphite URL to monitor, for example http://server/render?target=stats.auctionStart&from=-1minutes&rawData=true. When run, it will query that URL and treat the average of the values returned as the 'value' to be compared against the warning/critical thresholds, and return this value to Nagios as performance data. See Graphite's URL API documentation to generate the URL parameter.
You'll need to have NagAconda installed (e.g. easy_install nagaconda)