Maybe you want students to listen to information before they come to class. Maybe you want to make a recording available to them for review. There are many reasons to create podcasts. These articles provide practical tips and instructions.
How to Create and Deliver Audio Podcasts (advice from the University of Wisconsin about technique, equipment, and software)
Teaching & Learning with Podcasting (also from UW, matching your podcast to your teaching & learning goals)
Eight Basic Voice Recording Tips (from NspirD2, a teaching with technology blog from Notre Dame)