What makes a podcast different from an audio file?

It is the ability to subscribe to a podcast channel using a podcast "catcher" or "aggregator" program.

iTunes, or Juice are examples of podcast software.

In the case of iTunes you can just click on our Subscribe Using iTunes link.

In the case of any other podcast software you must copy the RSS link location into the "subscribe to new feed" box. In that case you can just put your mouse over either the icon or the RSS link, hit your right mouse button, copy the link location, and then paste the link location into the "subscribe to new feed" box in your podcast "catcher" program.