Insert a footnote on slides

Type the character you want to format as a footnote, then select the character and press Ctrl+Shift+= 

Go to Insert > Header & Footer.

On the Slide tab, select the Footer box, type the character you added in step 1, then type the footnote.

Select Apply.

In the new footnote at the bottom of the slide, select the footnote character and press Ctrl+Shift+=

Place the cursor where you want to add a footnote, then type the footnote character.

Select the character. On the Home tab, select (More Font Options) > Superscript.

Or select the character and go to Home > Font >  Superscript.

Select Insert > Footer > Footer.

Select the Footer checkbox, then type the footnote text. 

Close the Footer pane; when you do so, the footnote will be added to the current slide.