Rock Band 4's new instruments are getting broken in as we speak at E3, but Harmonix has outlined how new gameplay beats and how they're performed on the new guitars through an easy diagram.
The idea is that through experimentation, tapping or holding buttons (at the top or base of the guitar neck) as well as bringing the guitar upright, you can fire out different versions of notes, with on-screen indicators offering you opportunity to freestyle at certain song sections.