Podcasting is simply a handy way to deliver media rich content. This is where the internet is going.
You have free or paid content that you can download for cheap. You write up a nice little summary of what you get with a link at the bottom to download or purchase it. Oh, and it’s always nice to give folks a little taste of what they are about to grab.
An audio podcast is the recording of an audio track along with optional additional media like images, slides or movies. These are the easiest to create. GarageBand is a fine tool to use on Mac OS X.
A screencast is a podcast of you talking over a movie taken of your screen. You fire up the application you want to demonstrate and go to work showing off your cool new thing. While you are working, a screen capturing application makes a movie of everything you do. My favorite application for this is Snap Z Pro.
Most people record the audio of them talking while they are doing the demonstration. This is a nice example of a lecture on using the Grid System in HTML. If you find that process difficult, simply record the audio separately while reviewing the movie.
A video podcast is where someone comes in a takes a video of the actual participants. Most lectures are presented this way.
Here is an example of a video podcast that uses slides, screencasts and live video.