How to add text to a slide show in photos 3.0 running on my Mac with High Sierra 10.13.3

I have created an album with all the slides I want in it in the order I want, Then I click on slide show at the top of the album. I can click on themes, pick different styles "Ken Burns" etc and even add music.

This is the quick way to create an instant slideshow. But an instant slideshow is very limited. If you want to customize the slideshow with text and transitions, you need a saved slideshow as a slideshow project. Avoid the "slideshow" button in the album view.

Once you have collected the slides in an album, select the album in the sidebar (do not select the slides in the album). Now right-click or ctrl-click the album and use the command "Create > Slideshow" from the contextual menu, that will pop up.

Now open the new slideshow in the projects section of the sidebar. There you will find more tools to customize the slideshow.

To add text to a slideshow you have to add a title slide to each slide, that needs text, and enter the text manually.

In the film strip with the slides select a slide, then click the ➕ at the end of the film strip and click "Add text" Type the text into the text field.