Now you can insert footnotes in Google Docs by clicking on the Insert menu and selecting Footnote. “Footnotes appear on-screen in the document margin and at the bottom of the page when printed. You'll be able to see how the footnotes will appear when printed by selecting Print (Ctrl+P) or Download file as... PDF from the File menu. There will also be a footnote marker within the actual document designated by a pound sign (#). You can drag and drop a footnote anywhere you'd like in the document by simply clicking on this pound sign and dragging,” notes Google's help page.
Source:→ Google System