You can do a subscript in Google Docs by following these steps:
Open the Google Docs document where you want to add a subscript.
Select the text that you want to convert to subscript.
Click on the "Format" menu at the top of the screen.
Select "Text" from the dropdown menu.
Choose "Subscript" from the options that appear.
Alternatively, you can also use the keyboard shortcut to create a subscript in Google Docs. Just select the text that you want to make subscript, and then press Ctrl + , (comma) on a PC or Command + , (comma) on a Mac.
Your selected text will now appear as a subscript in Google Docs.