If you are completely new to computer programming start with the introduction and continue reading through the core concepts. Take you time and reread sections you do not understand. The best way to learn Javascript is to try it for yourself so follow along with the examples to the best of your ability. If you have programmed in another language before deciding to learn Javascript, feel free to skim the introduction and core section before focusing on the advanced section. If you have experience with Javascript before, go directly to the advanced section. This book can also be used as a reference as it contains many helpful internal and external resources for the seasoned Javascript developer.
The core examples are meant as a continuation of the concepts you learned in the core concepts section. To further your understanding it is best to run and modify these examples yourself instead of only reading.