Well, your podcast episodes have to actually live somewhere.
First, off, what the hell does hosting mean? Well, your podcast episodes have to actually live somewhere. Once you create a podcast episode using GarageBand (or Audacity) you need a place to save it (aside from your website and/or computer) so that the public can stream it or download it and listen to it. If you were to attempt to save these huge files to your website and then have people listen from there it would only be a short matter of time before your site crashed and people simply gave up trying to listen. So, we store our podcast episode files with a hosting service and can then link it on our website if we choose. Voila.