Embed a streaming audio player
You may want to add a preview of the audio file. You might also call this a "click and listen" version. You need to know the full URL of the where you have that media file stored. This must be a direct link to that file. In other words you'll need a site to upload the audio to that allows you to directly link to the audio files you've uploaded. Blip.tv is one site that lets you do this.
Once you have a direct link to the file then you can create an entry in your wordpress.com blog to stream the audio file with a flash player.
Create an entry which describes your file and add the following code within the body text of the blog entry.
[audio http://www.example.org/linkto.mp3]
This will look like this in the Wordpress interface.
Then click on "Publish" clicking on the button on the right.
Then when you look at your blog, if you have the flash plug-in installed, you'll see a player which you click on to play the audio file from your browser.
The player is quite basic but very functional.
Now that you have created a Podcast with streaming audio, you should learn how to find and promote your blog.