Load audio file on press of a button? Help!

Okay, so I just started using Arduino, and I have a project for my class due in a few days that I’ve procrastinated… anyway, basically I want to make an audio ‘keyboard’.

So the idea is, I would have 13 buttons attached to the arduino, and when you press a button, it tells processing to play an audio file (which will just be one note). So what coding would I need to make this possible? How do I load an audio file and make processing play it using the arduino?

And I know this seems really simple, and it probably is, I just have no idea what I’m doing, so if someone could help me that would be really great.