While this book is an important reference for Nmap, it isn't the only one. The Nmap web page at https://nmap.org is not just for downloads. It also provides substantial documentation from Nmap developers and third parties. For example, you can find the Nmap Reference Guide translated into a dozen languages there. Other books, videos, and articles covering Nmap are also available.

The official web site for this book is https://nmap.org/book/. Go there for errata, updates, and many sample chapters.

Any serious Nmap user should subscribe to the nmap-hackers mailing list for announcements about Nmap and Insecure.Org. Traffic is very light (about six posts per year) because it is reserved for only the most important announcements. Developers and particularly devoted users can also subscribe to the nmap-dev mailing list. Traffic is much higher (hundreds of posts per month), but it is a great place to learn about and try new features before they are released and to pick up tips from advanced users. Subscription information and archives for both lists are available at https://seclists.org.

While Nmap can be useful, it won't solve all of your security problems. Every few years I do a survey of thousands of Nmap users to determine what other tools they like. The list is posted at https://sectools.org, which has become one of my most popular web sites. Read through the list and you are sure to find many gems you had never even heard of. Most of the tools are free and open source.