1. How can I play back mp3 sermons?

If you open them on the browser, you can play them back by hitting play button. If you downloaded them to your PC or Mac, you need MP3 player software. For example iTunes or Windows Media Player.

2. How do I user RSS feeds - Podcasts?

Podcasts are channels, to which you can subscribe to have always newest MP3 sermons downloaded automatically This can be used on PC, Mac or smartphone.