Per PowerPoint help:
Add a summary slide to your presentation
If you want to include a summary of the key points in your Microsoft
PowerPoint presentation, you can use Slide Sorter view to easily create a
single slide that presents a list of selected slide titles.
On the View menu, click Slide Sorter.
In Slide Sorter view, hold down CTRL while you click the slides that have
titles that you want to include in your summary slide.
Tip Include only the slide titles that best summarize your presentation.
On the Slide Sorter toolbar (toolbar: A bar with buttons and options that
you use to carry out commands. To display a toolbar, press ALT and then
SHIFT+F10.), click Summary Slide .
If the Slide Sorter toolbar is hidden, on the View menu, click Toolbars, and
then click Slide Sorter.
The summary slide is created and added to your presentation.