Audacity: open source digital audio editor

Audacity Manual: a comprehensive guide to using Audacity.

The Free Sound Project: a massive library of downloadable and sharable sounds to use in audio projects.

Creative Commons Audio: another place to look for sound effects and music (with appropriate licenses that indicate how people should use and/or cite borrowed sounds).

Partners in Rhyme: contains public domain and royalty free sound effects and music.

Sound Bible: more free sounds

Jamendo: free music downloads

How to Extract Audio from Videos

How to Convert .mp3 to .wav files

Digital Millennium Copyright Act

Fair Use Doctrine