If your camera can record sounds, the sounds are digitized on your camera as a .WAV file with the same file name as the photo. If your photo has a sound file associated with it, it will be indicated in the contact sheet and preview window by a small speaker button.
You can play the sound by either selecting the speaker button or pressing the "a" key when a single photo with a sound file is selected. The "a" key will also toggle the sound off again.
In the Metadata (IPTC) Info window, the "a" shortcut does not work, but you can play sounds through the play and stop buttons.
You can delete the sound file by right-clicking (control-select) on the speaker button in the contact sheet and selecting delete from the contextual menu. You can move a sound file from one photo to another by selecting both the photo with a sound and the photo where you want to move it and right-clicking on the speaker button. If two photos are selected, the contextual menu will also give you the option to move the sound.