ACTIONSCRIPT 3.0 for AE and Flash CS5.5?

Good evening, I have no idea what's actionscript but I think it's cool. I'm willed buying a book but I have one here ( Flash CS4 The missing manual by Chris Grover) which has 7 lessons about Actionscript 3.0. Does it work for AE and Flash CS5.5? Do I have to buy another book? Which book you recommend? Thanks a lot again.