To insert a footer, in the Insert tab, click the Footer button.
The Slide Footer dialog will then appear for you to customize.
In the Date section, you can choose to automatically update the current date or add a new fixed date.
Check this box to insert a slide number.
And type a Footer name
Select this checkbox to not show the footer on the title slide.
Then click this button to apply the changes to all slides.
Now we'll see the result. 
This is the title slide, so the footer doesn't display on it.
Let's check the other slides.
The text is in white and too small to read.
So, we will need to customize it in the Slide Master.
In this master layout, we will select all the placeholders in the footer section.
Then style them in the Home tab.
I also change the color of the text in dark backgrounds to white.
Close Slide Master to save the changes.
Let's see what we've got.
That's it!
