This is a 10ft cable designed for Apple Dock devices that use the 30pin Apple Dock Connector. This type of cable is used to connect an Apple device to a television or other video input to output audio and video.
On one end is the 30 pin connector for the Apple device and on the other end are three RCA connectors. The red and white connectors are for stereo audio output (right and left channels respectively). The yellow connector is for a composite video output.
This cable allows an older iPhone (4s and earlier), iPad, or iPod to play videos on a TV screen, with the audio routed through the TV's speakers or an attached stereo system.
BONUS: I am also including for free an additional short cable that is a 30pin connector on one side and on the other side a USB Type A plug and a 3.5mm audio jack.