Should I learn different openings?

Right now I'm focused on 3/4 knight openings. To be honest I chose this opening simply because of how many people try to take an early rook/queen or checkmate in just a few moves. I'm getting the hang of it (generally).

I also work on the Sicilian Defense: Bowdler attack when playing white because it's works for me.

My questions:

1. What are the benefits of learning different openings?

2. Besides different openings, is there anything else that I should focus on (pertaining to the opening phase)?

3. I'm looking for a book that goes through openings in detail. Most of the ones I've found so far basically say "The following openings work" but don't do a good job of explaining why. Do you have any recommendations.

Sounds like you could use a general encyclopedia of openings type book for now.  Paul van der Sterren's Fundamental Chess Openings is a great reference with clear explanations that will get you to a playable middlegame.  Most openings he only gets 10 or 12 moves deep but at least you understand why those moves were made and what your general plan going forward should be.  No data dumps of unexplained moves in his book; van der Sterren will take a paragraph to explain one move.  A good book to start with although as you get better of course you need specialized monographs.

A1.  It increases your repotoire and you are prepared to play against your opponents openings.  You get to play different middlegame positions and hence improves your middlegame and chess.

A2.  Maybe you can find good responses to your opponents wrong/offbeat/not main line moves.

A3.  I have never read a chess book so I don't have any recommendations.  I watch people commentate on specific openings in chess videos and see people play it and sometimes go through an opening position my self and think about it in some detail.

(1) Innumerale benefits: you'll know which traps not to fall into, with each correctly placed piece you can boost your likelihood of survival maybe 2%, you'll be better able to detect when your opponent has fallen into a trap or misplayed somehow, you'll know better where to place your pieces, what plans to follow, what type of endgame to expect, which pawn formations to get or to avoid, which commonly winning tactics to watch for, which useful moves to play by default when nothing seems to be happening, etc.

(2) Yes, everything I implied in (1) since memorizing an opening is not sufficient. If possible you should learn: the *plans* or ideas behind each opening, including the small plans (e.g., outposting a knight at e5 in the Exchange French), the best places for each piece and pawn (e.g., f3 in attacks against Black's kingside fianchetto), common motifs (e.g., The Fork Trick), common traps (e.g., 3...Nxe4?! in the main line Petrov's Defense), the tactical shots that often win (e.g., Bxf7+ in Philidor's Defense), and how to win in the typical resulting endgames for that opening.

(3) Some well-known older books that are passable for describing the ideas/plans behind the openings are...

Evans, Larry, and Walter Korn. Modern Chess Openings.

Fine, Reuben. The Ideas Behind the Chess Openings.

Emms, John. Discovering Chess Openings.

...however I've never found an opening book I consider excellent. I'm finding I have to amass all the scattered information myself into what will likely become an online document someday, or maybe a book if I'm really lucky.

Youre not following the opening principles, youre hanging pieces, and youre missing simple tactics.  Forget about learning specific openings, and start following the opening principles:

Control the center

Develop toward the center

Castle

Study tactics...tactics...tactics.

y0u should play original openiings . Think for yourself, make m0ves in a board and then you check in internet if y0ur new ideas  have  names.  

For someone seeking help with choosing openings, I usually bring up Openings for Amateurs by Pete Tamburro (2014).

http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html

I believe that it is possible to see a fair portion of the beginning of Tamburro's book by going to the Mongoose Press site. Perhaps it would be appropriate to look at Discovering Chess Openings by GM Johm Emms (2006).

https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

"... [Fundamental Chess Openings] is not particularly suited for players who are just starting out. I would imagine players rated at least 1400-1500 would get the most benefit from this volume. ..." - FM Carsten Hansen (2010)

https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf

I think it is possible to read an FCO sample at the Gambit Publications site.

Thanks everyone, I'll check everything out. Just got chessmaster grandmaster edition and it helps train. After going through... 4 hours of training I think I've improved a bit. Now to go through 4 hours of 10 min games.

MCO10 was about half a century ago and most of it is lists of moves (in descriptive notation) without explanation. At one time, an algebraic revision of Fine's Ideas book was published, but much of it was from a time about two decades before MCO10. It does contain a lot of verbal explanation and was a very respected book for decades after it was first published. The Emms book is a very different sort of book that appeared about one decade ago, primarily attempting to help beginners understand opening principles.