This isn't really a PHP thing...
You have some choices, depending on the file format you want to use:
MP3's / MPEGs: simply upload the file to your server and call it from your HTML via a hyperlink.
The browser should pick up on the file extension and start streaming.
REALAUDIO: get a copy of RealProducer (free one available) and code your audio to .rm format.
Next you need to create a plain text file with the url of your .rm file in a single line at the top. Nothing else. Save this as whatever.ram
Then, call the .ram file from a link which will redirect through to you audio file and it should start streaming.
Otherwise, you might be looking at spending money on server-side streaming packages such as Shoutcast for MP3s or RealServer for realaudio. These might be necessary if you are planning on handling a lot of files & users.