SeeItDoItTV have created easy-to-follow video tutorials on how to create professional sounding podcasts using the free Audacity software. They also demonstrate some useful audio editing concepts like envelopes, converting stereo to mono, trimming and moving audio clips.

Most new podcasters get confused when it comes to choosing between mono and stereo formats during sound recording so these tutorials should clear all such doubts. Here's an excerpt from the tutorial:

The mono option will record your sound in one channel while the stereo option will record the sound in both left and right channel. This means the same sound will be duplicate in the right and left speaker during playback.

Since podcasts are mainly voice with a little bit of background music, mono option is recommended which will also produce small MP3 files.

The tutorials are split into two parts:

Audacity Tutorial One - How to record your first podcast using Audacity.

Audacity Tutorial Two - How to edit and enhance your audio (Cut, copy, splice, and mix sounds together and change the volume speed or pitch of a recording).

Must watch for all budding podcasters. [Thanks Vinu]

Related Podcast Reading:
  Podcast Recording Tips for Beginners
  How to Choose a Podcast Host
  Where to Download Podcast Music