With the Seriously Simple Podcasting plugin installed and set up, your podcast episodes will be available at this URL on your site: http://www.example.com/podcast and your feed will be available here: http://www.example.com/feed/podcast.
You can also set your podcast episodes to appear in your home page blog feed in the general settings. If you've elected to use Castos hosting, the media files aren't stored in your Media Library, since all of the audio files will be stored in Castos.
If these URLs do not work for you, re-save your site’s permalinks by going to Settings Permalinks in the admin menu and clicking on the save button.
Your permalinks will need to be set to anything other than default for this to work.