I learned from a book called "Idea Mapping" by Jamie Nast. That's also how I discovered MindManager, which I could not live without. I think it came with either a cd or instructions on how to get a free trial.
Both Mindjet and The Brain have tons of helpful resources on their sites. Michael Deutch at Mindjet is super helpful, too. As an aside, I'm working to get Shelley Hayduk, writer of The Brain's blogsite, as a guest on a future episode of the GTD Virtual Study group.
A great resource for any kind of mindmapping (Digital or Analog) is The Mind Map Book by Tony Buzan author of Use Both Sides of Your Brain. The Latter book was my introduction into mindmapping, which allowed me to see the big picture of any project that I attempt.
I use Mindmanager Pro ver 7.0. I've been with Mindmanager since ver 3.0 when it was known as Mindjet.