__Underlined__ words are links to external resources. When also __Italicized__, they probably link internally to other parts of the book. Their text usually indicates where. In the ebook or online, just click them. They can also be titles of downloadable books.
You needn’t read this whole book just to get the idea. I present it in layers: immediately in brief, then in detail.
The book is an integrated whole, best read cover to cover, including the blurb, foreword, etc. Each section builds upon the last. Every word contributes to understanding.