I'm not sure why Apple didn't elaborate on this feature some more since it is actually useful! It's really useful for any txt hvy tween who wants to sound like a mature, older adult.
http://lifehacker.com/5849229/how-to-configure-ios-5s-awesome-built+in-text-expansion
http://lifehacker.com/5849229/how-to-configure-ios-5s-awesome-built+in-text-expansion