Sailboat Types

One of my hobbies is sailing and sailboat racing, and all of my time talking about, working on and being out on the water, I have never been able to memorize the name of each boat configuration.  What is the difference between a ketch and a sloop and a Gaff rig.  Well I found this article which explains the differences pretty well.  Even though I found this article, I doubt I will be able to memorize them.