Determine the method of playback for the guitar backing track. The device used to play the backing track determines how to patch the audio signal into the amplifiers. The best method is to play it on a portable or home stereo. These units may still have the older 1/4-inch jacks used for headphones; just use a cord with 1/4-inch male ends and plug one end into the headphone jack, the other into the low-gain, or clean, channel on the amplifier
Connect the playback device to the amplifier using jack adapters. Most head phone jacks today are smaller than 1/4-inch. Adapters can be purchase at electronics stores, such as Radio Shack, as well as online. To make the transition, use cord with 1/8-inch ends, plug one end into the headphone jack on the playback device, and the other into a 1/8-inch to 1/4-inch adapter, which then fits into the amplifier's input jack.
Play the backing track through the amplifier. Just play the device as normal, and the sound can be adjusted using the controls on the amplifier. Plug your guitar into the high-gain channel. Adjust the guitar volume as well as the backing track volume to get the proper levels.