Book on Openings

How to Play the Chess Openings by Eugene Znosko-Borovsky. It is an old book in descriptive notation and the opening lines are dated, but the brief explanations are good and sufficient for most of us playing casual online speed chess.

For learning opening fundamental principles the best book (IMO) is "Discovering Chess Openings" by John Emms. For a single volume openings reference presenting the details/moves of most of the popular and major openings I recommend "FCO - Fundamental Chess Openings" by Paul van der Sterren.

Good Chess Openings Books For Beginners and Beyond...

https://www.chess.com/blog/RussBell/good-chess-openings-books-for-beginners-and-beyond

Good Chess Books for Beginners and Beyond...

https://www.chess.com/blog/RussBell/good-chess-books-for-beginners-and-beyond\

As for the recommendation of Znosko-Borovsky's book (ref post #2 above). Although It is an instructive, well written book, I would not recommend it for an absolute beginner for two primary reasons. First and foremost, the book (which was origninally published in 1935) is written in the older, (and now essentially obsolete) "Descriptive" notation. The issue with that is that, especially for beginning chess players, Descriptiive notation can be very confusing to learn in comparison to the current standard, "Algebraic" notation. For those who are comfortable with Descriptive notation, that may not present a significant impediment. However, the point is that becoming comfortable with Descriptive notation tends to be an impediment for those with no prior experience with it. The second issue with Z-N's book is that having been written some 90 years ago many of the specific opening lines and variations (i.e., the 'theory') presented may be out of date, although the fundamental concepts described may continue to be valid,.

https://en.wikipedia.org/wiki/Descriptive_notation

https://www.chess.com/forum/view/general/descriptive-notation-vs-algebraic-notation

The bottom line with Z-N's book: His writing style and explanations are very accessible to the beginner. In fact I enjoy reading his books on that score alone. The impediment is primarily in the use of (the cumbersome) "Descriptive" notation compared to the modern standard, "Algebraic" notation.