I think you mean "rock out." This just means that a musician is playing loud rock music and getting very "into" the music or showing a passion for the music while they play.

This phrase is only found in Avril Lavigne's, to thebest of my knowledge. It isn't a common expression. It means she turned on the TV and was surprised to see the boy she used to know being a big celebrity. A similar expression, "rock on", is very popular, and means "go get it", "do it" etc.