You don't say what version you're looking for, but if you look at the documentation at docs.jivesoftware.com, you should find the topics you're looking for under Community Administration, Platform Administration, and so on. Documentation for each plugin compatible with your version (such as Fathom) will be listed in the left pane of the Help system. I hope that helps.
I'm *brand new* in Jive and just downloaded the Fathom app. Trying to find out how to use it, but can't figure out where to find documentation. How do you navigate to the link docs.jivesoftware.com? I typed in the url in a new browser window and it doesn't work. And, do you know if the trial/download version of Fathom is feature limited?