Audacity is a free sound recording and editing program for Windows, Macintosh and Linux. It's a useful tool for narrating your web videos and multimedia. An alternative to Audacity is Apple's GarageBand software, which can be used for sound recording as well as music composition.
It's useful to note that uncompressed audio goes by two names -- WAV files and AIFF files. MP3 is an audio compression format that creates audio files 10 times smaller than WAV or AIFF files, without much loss of sound quality.
There are many ways of creating MP3 audio files using free software, including Apple's iTunes software, available for Mac and Windows. Better sounding MP3 have a higher "bit-rate" than poorer sounding MP3 files. Many people use 128 kbps as bit-rate for their MP3 files. Any bit-rate higher than 192 kbps sounds almost identical to the original uncompressed audio file. A bit-rate of 64 kbps (or less) sounds blurred or "muddy."