Agent client collector - updating Operating System field

We have been testing the agent client collector for servers and workstations that are not routinely available when Discovery scans IP segments.  The basic setup is not hard and seems to work, but I'm having a hard time understanding how to create a "check" that will return the Operating System field and populate it.  OOB, I guess it's 'enhanced discovery' that populates OS Version, RAM, and others, but not that specific one.  I'm sure there will be other data people ask for too.  SN documentation takes me around in circles, stating that I can make my own checks, which is great.  But nothing on the command structure and how to map whatever is returned to fields.  I understand that the Ruby language is used, which I'll have to study up on.  But I'm just not finding anything that helps me make one that gathers the data and injects it into the right end point.  Anyone have a guide that can tell me how to create such?  SN documentation seems to tell me 90% of what I need to know, but leaves out key pieces of information that would be really helpful.