Where the hell do you start?
The best thing to do is get your ass down to an Apple store and do one of their introductory workshops. It lasts two hours, you'll get a great overview and you'll be able to ask questions. It's perfect, however I will say that the tutor at the workshop I attended had problems answering some questions about FCPX and also had no professional experience as an editor.
If you're near the Covent Garden Apple store you might want to take advantage of the ProLabs series. This is an 8 hour FCPX course and it's absolutely free. I've just booked myself on the next one, so I'll let you know what it's like.
If you're not near an Apple store, don't worry, there are plenty of great online tutorials:
Larry is probably the most knowledgeable of all the FCPX tutors I have watched. He knows everything and is very good at describing every minute detail of FCPX. I love Larry and you could do a lot worse than watch his tutorials if you want to get into FCPX. My only criticism is how long he takes to get to the point!
Comprehensive and well executed set of tutorials.
There's a pretty good set of free tutorials Izzy's website.