Apple released an update iMovie at the same time is released their Mavericks OS. While the interface is slightly different, all the options are still there. Below are some tutorials on the basics of using the new iMovie. Personally, I think that many of the updates are improvements on the program.
Using a Green Screen: More detail
A details tutorial (long too) but I even came away with some great ideas.
Slideshow courtesy of Mr. Mortensen