This book is perhaps the best introduction for the novice currency trader. Each chapter in the book is short, very straightforward, easily digestible, and full of information. I also like the cautionary attitude the writers of the book have: they warn you about leverage, [...], and illusions of making easy money.
This book should be the first book you purchase and read thoroughly if you are interested in online currency trading. However, you will have to find other books and references once you start (or rather before you start) trading online to gain more knowledge.
More experienced traders (in stocks, options, etc.) will find this book less valuable but this is a little gem for an absolute beginner.