Dan and Erin Ries are two amazing instructors who are so skilled at teaching and break everything down into such detail that the moves become easy to learn. How they describe things really makes you comprehend the techniques.
Part 5 switches to the no-gi side of things, and how to start getting some subs from the top. The armbar from mount is an essential technique, but often people mess up a lot of the details. This is perfect against opponents who are larger than you.