The most popular free program (by far, with probably about 99% of users choosing it) is Audacity:
http://audacity.sourceforge.net/
If you download Audacity you need to be aware that, in its native form, it can't save files to MP3 formats. (That's due to licensing issues). However a few extra clicks of your mouse will enable you to download and install the LAME MP3 encoder, which fixes the problem:
http://audacity.sourc...?s=install&i=lame-mp3
I'll suggest one further download associated with Audacity, and that's the User Manual. While Audacity is a fairly intuitive program, it can be easy to spend ages trying to work out how to carry out a simple task which could have been done almost instantaneously by simply reading the instructions. I write from experience ;-)
http://audacity.sourc...et/help/documentation
Chris