There is really a lot more to jazz than a website if you want to "get a really good command over the style." *Of course there are books and teachers and classes you can take, which will all help. *But one thing I strongly suggest is picking out some jazz players you really like and listening to them day in and day out. *Learn their songs, and this, accompanied with theory, will get you thinking the right way.
Try
www.jazzguitar.com.