Greetings AmyS1965,
If you are having difficulty creating a slideshow in Photos on your Mac, begin by following the guidance found here:
Create slideshows in Photos on Mac
"Add or remove photos and text in a slideshow
After you create a slideshow, you can add or delete photos at any time. You can also add text to selected slides. The text position and font is determined by the theme you chose. When you add a Live Photo to a slideshow, it appears as a still image.
- In the Photos app on your Mac, click a slideshow under Projects in the sidebar.
- Do any of the following:
- Add more photos to a slideshow: Select a photo in the row of thumbnails at the bottom, click , then click Add Photos. Select the photos you want to add, then click Add.
- Add text to a slide: Select a photo, click , then click Add Text. Select the text in the text box, then type the text you want.
- Delete text from a photo: Select the text in the photo or select the T frame before the photo in the row of thumbnails, then press Delete.
- Delete a photo from the slideshow: Select the photo you want to delete, then press Delete."
Take care.