If you have an audio file and you want to play it, you can just call Device.Media.PlayAudio() and provide the relative path of the file. Of course, the file should be in the resources folder as you should remember from the file management tutorial.
If you want to use the microphone to record the user's voice or the surrounding sounds, you can call Media.AudioRecorder.StartRecording(). For example, when the button is clicked.
byte audiodata = await Device.Media.AudioRecorder.Stop();
End listening and recording, then you can stop recording and get the results, you can call the AudioRecorder.Stop() method which returns the audio data. You can then save it locally or upload to an API or do what you want with it.