I don't think a book is the best way to learn this stuff. I recommend the hands-on trial and error process. Start with the blink sketch(File > Examples > 01.Basics > Blink). Go through the sketch line by line and make sure you understand what everything does. If there's something you don't understand get on Google and start searching until you do. The Arduino reference page has a lot of information but don't limit yourself to only that one. You're going to find some bad information mixed in with the good but this is a valuable lesson in itself. Don't just blindly believe anything you read, whether on the forum or in a book. You need to develop the ability to search for information efficiently and critically evaluate the results. At first this may be a slower process than reading a book but as you progress in your explorations internet searches will inevitably become your primary source of information so you might as well use it from the start.
Next, use your understanding of the Blink sketch to make some modifications. Make the LED blink faster, make it change blink speeds, make it blink randomly. You can actually have a lot of fun with just a simple LED.
Continue this process through the examples. You don't necessarily need to do every example as some may deal with subjects that aren't useful to you but definitely learning the basics like digitalWrite(), digitalRead(), analogWrite(), analogRead(), debouncing, and Serial.print() as well as general programming functions are essential.