Essentially, listening to a podcast is like listening to a radio broadcast. Podcasting is a newish way of communicating. A podcast is a media file distributed by subscription over the Internet using syndication feeds for playback on mobile devices like iPods (hence the term) and personal computers. They started to become popular back in 2004 and
Podcasts have really only been around for the last few years. Wikipedia has an interesting article on the history of podcasting.
Though podcasts are basically sound files, you can insert photos using a program like GarageBand. These photos can help you illustrate the information in your podcast.