RCA cables are still in use today, though they were invented over 60 years ago by the Radio Corporation of America (the company that had little dog looking into a phonograph for a logo). Originally made for use with home stereos, they allowed consumers to connect their phonograph players and radios. Their design has been adapted over the years to conduct not only audio, but video as well. You can use them to connect stereos to televisions and televisions to gaming consoles, DVD players, or any other compatible device. There are two basic types of RCA cables, which have colour-coded tips, so plugging them into the correct jacks is quite simple.
When buying RCA cables, there are two basic sorts. There are those that have only the red and white plugs, used for audio only, and there are those with the third, yellow plug to connect video as well as audio.
For home theatre use, RCA cables are generally of three colours. The yellow is the video plug, which should correspond to a jack on your DVD player, VCR, gaming console, television, or other device that's ringed with yellow.
Red and white
The white and red cables are audio cables. The white is designated as the left speaker (and mono, in the case that the media you're using isn't in stereo), and the red is the right. The colours don't matter in terms of the cable's function. The twinned cables are identical, but they are colour-coordinated to allow for more control over where the sound is going.
Video cable substitution
If you're desperate to watch that old home movie at your grandmother's house using an old television and VCR, you will have about the same signal if you use audio plugs in place of the yellow video plugs. Just make sure your colours line up. You could use the red plugs to connect the yellow video jacks from the VCR and the television, in other words. While these cables can't conduct high-definition video, they'll do in a pinch, no matter the colour on the end of the plug, and you should be able to hear enough with one audio plug connected. The longer the cable is, though, the more the signal will degrade.
Connecting different technologies
Some devices might call for another sort of plug on one end, while using the standard RCA plugs on the other end. For instance, a newer innovation called the Scart plug, might be compatible with one device, while traditional RCA plugs are needed on the other. If you lack the proper cables, you can buy adaptors, making it possible to continue to use older and newer technologies together.
WIth surround-sound systems, it might be necessary to coordinate multiple colours. If you lack a manual for your system, those tangles of RCA cables you might have could be a little confusing (see Resources). Regardless of how complicated your system might be, though, the basic usage remains the same: colour-coordinate.
Inputs and outputs
Many devices have jacks for audio and/or video in and audio and/or video out. Remember, the device that's generating the media is the one you'll use the "out" jack on. For instance, on your DVD player, you'll plug your cables into "DVD Out." The yellow video cable will correspond with your television's "Video In" jack, which may not be marked, other than by a yellow-ringed jack, since your television might not be made to feed out to another device.