Joomla extension development.

Does anyone know of any great resource for learning to develop joomla extensions. I have my php skills in tact but I can't seem to find any good resource on how joomla code works. On YouTube, the only videos I can find are those where an elderly guy, I think his name is Robby, discusses how to develop MVC components. I think he must be doing a great job, but the videos are in too many parts that seem to put me to sleep. Any good recommendations?