As a verb, "rock" means "to sway". It is also a slang meaning "to be very good, impressive, exciting, or effective" (dictionary.com). It is in this sense when they say "I want to rock" or "Do you want to rock and roll". It is like "Let's get started (for something exciting)", "Let's have a ball". and so on.

I wanna = I want to Rock and rock & roll are music genres So I wanna rock = I want to listen to rock music Good luck I wish I could help you