Attach the 1/8-inch adapter to one end of the 1/4-inch cable. Either end of the 1/4-inch cable is fine to use.
Plug the end of the 1/8-inch adapter into the CD player earphone jack. The earphone jack may be labeled with the words "output," "headphone" or with a picture of headphones.
Plug the 1/4-inch, non-adapter end of the cable into the input jack of the amplifier. The input jack will be labeled as "input" or it could have a number "1" next to it.
Turn on the amplifier. Keep the volume turned low at first and adjust it up. This will avoid any sudden loudness.
Turn on the CD player. Keep the volume level on high, or as close to high as possible without distorting. This will send a full signal to the amp, and you can adjust the overall volume level from there.
Press play on the CD player to play the music through the amplifier.