Audio post format
If your post contains audio, then you should use this post format. Select Audio in the appeared metabox and add link to your mp3 file.
Status post format
Donec dictum libero vel orci malesuada mattis. Suspendisse libero ante, varius ac laoreet vel, blandit eget lacus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; …
Aside post
Aside post format.