Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
The material in this book is the least linear of any Mac book I've ever written: there are few interdependencies among the topics, so you can start with any one that piques your interest or is likely to answer the burning questions you have about using Safari—whether they're of longstanding duration or specifically about Safari 4. Luckily, ebook links lend themselves to just that sort of approach!
On the other hand, if you don't want to accidentally miss anything, just follow the advice given to Alice: "Just start at the beginning, and when you get to the end… stop."