I use the videos that Mac provides on their websites as a first step. Then I play around with the applications. If I still need help, I buy a book. I usually have to have one of my books nearby because these aps have so much build in.
I've found that learning by doing has been the best way for me and when I deliver any training to other staff I encourage them to play with the software on their computer, Mac or PC.
I've found that with iMovie especially the only way I got to grips with it was to keep doing stuff until I figured out the quickest and best ways!
Aloha Lisa,
Although they can be boring if you watch for too long, Atomic Learning http://movies.atomiclearning.com/k12/home has short video clips of anything and everything mac or pc related. Site licensing is pretty reasonable. You can also use the tutorials from Apple. Good luck.