Exactly how does the iCal bit work?

I'm trying to figure out why the iCal icon doesn't give me what I expect. If i'm looking at a particular event, I would have thought that clicking that would give me an iCal download for that event that I could then import into, say, Outlook. But that's not what's happening. Instead, sometimes I get an error message, and sometimes I get a completely different event. So, if someone could explain how this feature is supposed to work, that would be great! :-)