Insert music
(You can choose a piece of music from file (something that's stored on your PC) or from a CD if it's in your PC or record yourself singing/speaking if you have a microphone)
There will be a little speaker icon where the music plays from (see top left hand corner of this picture). When the sound uploads to powerpoint it'll ask you if you want it to start automatically or on click (it is sometimes easier to start it on click)
Rehearse timings:
This will allow you to play the music/sound throughout the slides.
Good luck Ciara! I hope this helps!