In reply to Nina Phillips.

So an audio (podcast) host is most often a service which has nothing to do with WordPress. You set up an account, and you interact with their dashboard. They host your audio and serve it up to podcast players. You can embed the podcast from these hosts into your WordPress website easily enough.

Castos (with their Seriously Simple Podcasting plugin) is a little different. Once you've set up the account you can do all-the-things via your WordPress website. It's all handled as metadata in the Podcasts Custom Post Type.

There's benefits to both models, but Joe clearly like the Castos model.