In order to play your audio file(.mp3) in Layar, firstly, you need the audio file to be hosted on a server. It is possible to host your .mp3 file on the site http://kiwi6.com/
After you uploaded your file, you will see the following page, by then, click "saved link"
You will see this locating at the right side of your page after your click
Please copy the "Direct Hotlink" and use this link to create a audio button in Creator.