The genomed service is a simple web app that serves as the canonical source of Genome machine information used in compiling puppet configurations. It's really quite simple so it's probably best explained by simply showing the link: http://[your repo hostname]/genome/nodes.html. From there it should be simple to browse find the other features by exploration.
It's also worth noting that most of the resources (this is a RESTful service) have several representations. Try changing the urls to end with xml
or yaml
.