Sound files are in MP3 format. You will need an MP3 player, which you can download free.
Try QuickTime (PCs or Macs) or WinAmp (PCs only).
Study tip: To record your responses use your computer microphone or a headset and open Sound Recorder, a free Windows program. (Click on the Start button and go to Programs › Accessories › Entertainment). You can also download free Audacity, a sound editor, player and recorder (PCs or Macs).