I have only the Playback tab in Lightroom slideshow. When I click on the select music it will only add one song and plays that over and over. There is no + sign to add additional tracks. If I hit the select music tab and add another track it just replaces the one I first selected. Lightroom 5.7.1. There also are not any lightroom templates preloaded.
Multiple tracks will have to be created in other software so that you have a single file that contains all of your music. Then you can use that track in your Lightroom slideshow.
Why do the tutorials all show an option for multiple tracks by hitting the plus sign next to the duration button?????
Support for multiple tracks (up to 10, I believe) was a Lightroom 6 feature.