One of the great things about the Raspberry Pi is how everyone starts with the same piece of gear. Since the audio hardware is identical on every unit, it is trivial to load the drivers and play mp3 files.
This guide describes how to connect input buttons and play audio files using a Raspberry Pi running Raspbian. We make use of Adafruit's Pi Cobbler and the Python module RPi.GPIO.
If you have not already used the Raspberry Pi as a input device this guide will show you how to wire the pull-down resistors, GPIO pins, and buttons.