How can I play music using a speaker and Micro SD card Module?
This Arduino project is one of the most simple and fun projects you
  can build with Arduino in 10-15 minutes. The result of this make will
  be an Arduino Audio Player which will play “.wav” files. It consist of
  a speaker, a simple transistor acting as an amplifier and a micro-SD
  card adapter with a micro-SD in it through which the .wav files are
  loaded and played.


https://diyhacking.com/arduino-audio-player/