Speakers are available in many shapes, sizes and colors and work in the same manner as stereo speakers.  Some computers may come with internal speakers, which is especially true to laptops.  If a computer is equipped with a sound card, then you can attach external speakers through a jack located on the sound card.  If a CD-Rom has a headphone jack located on its front, then speakers can be attached at that location.  Speakers usually come in pairs, but can be hooked up like a stereo system, including right and left front, right and left rear, a center channel and subwoofer.  Speakers generally have the volume and tone knobs located on their front panels.