IM Jeremy Silman recommends Fundamental Chess Openings (often abbreviated FCO) as a good one volume introduction to chess openings.
Having said that, lower level players should not spend much time on opening theory. A little is ok, but there are other things that will help your game much more at this point. You should know good general opening principles, like control the center, develop your forces, king safety, etc, but you shouldn't be trying to memorize alot of opening lines.
The reason being, for a new or improving player, games are going to be won or lost on tactics, plain and simple. Learn baisc tactical motifs like pins, forks, skewers, etc, and solve tactics puzzles, like the tactics trainer here at chess.com or the tactics problems available on a number of other sites. You need to develop the ability to keep your pieces safe, see the enemy threats, and see where you can threatened the enemy. Once you are able to do that you need to be able to calculate combinations of moves at least a few ply deep.
Learn a little endgame theory as well. At absolute minimum make sure you know all the basic mates.
When you do look at opening theory, don't just memorize moves. You have to try to understand what is going on and why the moves are being played. I often say that it is better to know five lines with understanding than to know fifty lines by route memory. In lower level games either you opponent will pull out a line you haven't studied, or will not know the theory themselves and will just start making things up. In either case you need to have a sense of why you are making the moves you are making, so you can find a sound way forward once you have to start improvising, which is often quite early in low level games.
Edit: By the way, I am still very much in the improving player category myself, and in the last couple of months I have been able to raise my correspondence rating from under 1200 to 1430 by following this advice. Down in patzer land where I play it usually comes down to tactics, and in the few cases that it doesn't the matter is typically resolved by endgame skill. When I win it is because I avoid serious tactical errors and notice when my opponent gives me tactical opportunities. When I loose it is generally because the opposite is happening.
I am a relative novice to chess and would like a good book or program to be a bible that i can refer to, to learn about the various openings that people use and improve my own games. Can anyone recommend anything for me?