The private lessons are described here with some example lessons: private lessons
Think of it like walking into your local music store and taking lessons from the resident guitar teacher. You simply tell him what skill level you are at and what you want to learn. Except after the lesson is finished, it will all be archived for you using the Riff Interactive tools including synchronized tab, video, jam tracks, and text descriptions.
Regarding music categories, we don't currently have a teacher that specializes in jazz-fusion exactly. We are currently recruiting teachers with specialized skills and hope to have hundreds to choose from some day. Let us know if you have recommendations :-)
I hope this answers your questions in some way at least. Let me know if you need more clarification.