Hello there, Brenda.
It sounds like you're rearing to go and create a slide show project in the new Photos for Mac. The following link to the online Photos Help Guide provides how to get started:
Create and work with slideshows - Photos Help
Create a slideshow project
Select the photos you want in your slideshow.
You can add or remove photos later (see “Add or remove photos and text,” below).
Click 
in the toolbar and choose Slideshow.
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 click a theme.
You can change the theme at any time. The theme you choose determines the text position, fonts, and the transitions that appear between slides. The pan and zoom effect, also known as the Ken Burns effect, is available only for the Classic and Ken Burns themes.
To select music for the slideshow, click the Music button 
, click the down arrow next to Music Picker, then select a song or songs.
Choose Theme Songs from the pop-up menu to see music included with Photos, or choose iTunes to see music from your iTunes library. Drag the songs you selected to change the order they play in. To delete a song, select it and press Delete.
To change how long each slide appears, click the Duration 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 a transition for specific slides: Select the slides you want to specify a transition for, select the Transition checkbox, then choose a transition type. Select any options (such as speed and direction) for the transition you chose.
Set slides to fill 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 
.
To play the slideshow, click the Play button 
.
To stop playing a slideshow, press the Escape key. You can also press the arrow keys to skip forward or back through the slides, and press the Space bar to pause the slideshow.
Thanks for participating in the Apple Support Communities.
Cheers,
Pedro.
