Go to your first song slide and show the Animation Pane open.
Right-click on any of the animations and Hide Advanced Timeline.
You should now see the mouse icon for your animations.
Go to Student Share > Koppejan > MUSIC > and open the folder for your year.
Select the song file from the folder and drag it onto the top-right part of the song slide. Make sure it's in the upper right corner so it's out of the way.
With the song icon still selected, go to the new Playback tab on the far right.
Click on the Play in Background button. This makes it start playing automatically, for more than one slide, and it hides the song icon when watching the slide show.
In the animation list, right-click and choose Effect options...
This will will open the Play Audio window - the song is set to stop playing after "999" slides.
Make the song stop playing after 2 slides and say OK.
Repeat for each song slide:
On your slide, click on the song icon on the slide and go to Trim Audio. Does each song start in a good place or is there a better place to start?
Drag the green slider to where the song should start. Do not move the red slider!