I am no expert, but since nobody has answered, I'll take a stab at it. I believe if you have the audio track selected, you can split it at the playhead. If the portion you want to start playing is immediately after the split, then simply delete the first portion of the sound clip, and place the remaining portion of the track where you want it to start within the movie. If the sound clip is a part of the movie itself, then use the extract audio feature to separate the audio, and then split it. Hope that makes sense...
Mike