Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems.
Step 1. Download it free at your home, from their the Audacity Website.
Step 2. In order to create, mp3 files you also need to download the lame encoder (also free).
Teacher and Student Resources:
Quick Reference two page handout
Check out a basic, introductory Teacher Tube video about Audacity
Digital Resources for using Audacity & Great Podcasting Info
Audacity Samples - Books, Articles, Assignments