You can learn a lot just by trying it, and then, when you have a SPECIFIC question, search on Google for it. There are answers in places like:
Here, this forum
The Codex documentation links (helpful to search google for your question plus the word "Codex")
WordPress Weekly Podcast, and WP Community Podcast
Searching Google for "wordpress tutorial" and whatever area you're interested in.
The problem with books is, they are usually written on an out-dated version of WP. And they can't fit all question-answers in a book, they have to guess what your needs are.
Many many more good (and free) answer links,
hope this helps ya