This option lets you select specific characters that it’s possible for you to’t otherwise add in Slides.
When theInsert Special Charactersmenu box appears, typeSubscriptorSuperscriptinto theSearchbox.
Your specific search will bring up a selection of menu items to choose from.

In this example, we entered Subscript.
go for the search result option you want to use.
Slides will automatically add it to your document wherever you have placed your cursor.

That process reverses the actions used to add superscript or subscript to your slide.
Why Use Superscript and Subscript?
Here are some examples:
