Here is the default way of adding a podcast episode to the playlist.
When you add an episode to the playlist, it appends at the end of the play list and waits for its turn. If playlist is empty, then by default Ziepod does not play this newly added item. If you want it to play, then check corresponding customization help topic.
You can also set Ziepod to add newly detected or downloaded podcast episode automatically. To learn more, check the corresponding related help topics.