I've heard that to get the best sound from my speakers, they need to be "in phase" when I hook them up. What does that mean?

When your stereo speakers are connected in phase, the drivers of the left and right speaker move in and out at the same time. When they're out of phase, the drivers of the left speaker move in, while those of the right move out. If your speakers have removable grilles, you can pop them off and actually see this.

Stereo speakers should always be connected in phase. Out-of-phase speakers sound "not quite right" — imaging is vague and there isn't as much bass.

To hook up your speakers in phase, just make sure that your positive receiver (or amplifier) terminals are connected to the positive speaker terminals, and your negative receiver terminals are connected to your negative speaker terminals.

It helps to pay attention to the markings on the wire — look for print, a stripe, or a rib that may be molded into the wire's jacket. If you find that your speakers are out of phase, don't worry, it's easy to fix. Just switch the positive and negative leads at one of your speakers (not both).