This is a sound pack that replaces the new bow sounds added in 6.0 with the old pre-6.0 bow sounds.
To install it, just extract the downloaded zip and copy/paste the Sound folder into the main WoW directory. If it asks if you want to merge folders, click Yes. Do not install via the MMOUI Minion or Curse Client as they will try to install this as an AddOn (which won't work).