You can add or remove photos later (see “Add or remove photos and text in a slideshow,” below).
Choose File > Create > Slideshow > Photos.
Click the Slideshow pop-up menu and choose New Slideshow.
Type a slideshow name in the Slideshow Name field, then click OK.
To reorder photos, drag photos into the order you want them in the bottom of the window.
To select a theme, click the Themes button , then do any of the following (not all options are available for all themes):
Set the slideshow to match the length of the selected music: Select Fit to Music.
Set a specific display time for the slideshow: Select Custom, then drag the slider to specify how long the slideshow should play.
Set a transition for the entire slideshow: Select the Transition checkbox, then choose a transition type from the pop-up menu.
Set slides to fit the screen: Select the “Scale photos to fit screen” checkbox.
To see a preview of the slideshow, click the Preview button.
Click Preview again to stop the preview. You can also set the slideshow to loop continuously by clicking the Loop button Export photos, videos, slideshows, and memories in Photos on Mac