ergative + another introduction

What exacly constitutes ergative structure?  I've seen it mentioned numerous
times but I am completely in the dark as far as how it works.  Is there
perhaps a website someone could link me to, or do any of you want to enlighten
this poor soul about the mysteries of the ergative structure?

Thanks,
Erich

p.s.  hmm, I still haven't really introduced myself.  My name's Erich
Kummerfeld, I'm an American College student, I'm 19 years old, I go to
Hampshire College in Amherst, Mass.  I've only recently gotten really sucked
into linguistics and conlanging.  I haven't made any conlangs of my own, in
high school I spent a good year and change constructing a conworld with
numerous concultures, drew up some detailed maps, wrote histories, designed
cultures and weather patterns etc.  That's essentially the limit of my con-
anything experience.  I took French for a few years in highschool, then took a
very intensive course in Japanese for my senior year, and took a semester of
Spanish recently.  I'm a native speaker of English (obviously).  At the moment
I'm mostly trying to learn as much as I can about the different kinds of
languages, both constructed and natural, as I can as well as people's theories
and strategies of creating conlangs.  I'm starting to compile a list of
properties that I would like my conlang to have, if/when I make it.  I suppose
the primary one right now that I'm thinking about is word efficeiency or,
since words can be incredibly large at times, syllable efficiency, i.e. a
person should be able to communicate a variety of complex thoughts without
spending a large amount of time speaking.  And I'd like to figure out ways to
do this without having a grotesquely large number of phonemes, as I have other
ideas about what kinds of properties I'm looking for in a set of phonemes.

that's a goodly amount of stuff.  It's always fun when the postcript is four
times as long as the actual message.