Footnotes at the bottom of a page can be used to provide references or additional information such as an explanation or clarification.
I am not a fan of footnotes at the bottom of a page as they don’t contribute to clear communication. It is distracting for readers to leave the text, go to the bottom of the page to read a note usually in smaller font, then try to return to their place in the text. Then repeat several times on a page. And on the next page and the next.
When considering footnotes, ask yourself: How important is the information? If it is very important, worth saying and you want readers to read it, then put it in the text, not as a footnote. If it is not important, leave it out. This suggestion applies to both brief, infrequent footnotes and longer, more frequent footnotes.
For footnotes which are references, consider using the author date style for referencing in the text. If important explanatory notes are required, consider listing them either at the beginning of the document or at the end of the chapter or document.