Your Google Doc must be in pages format for you to add footnotes. Click wherever you want to insert a footnote on your Google Doc, then click Insert from the top toolbar.

It will add the image to your page, plus a superscript number and a source link to the bottom of the page. To delete a footnote, simply delete the superscript number in your text.

You can add page numbers on Google Docs to any document. All you need to do is go into a document's Insert menu, which will give you several options.

Learn how to add images captions to Google Docs by reading this guide.