Place your cursor at the end of the word or sentence where you would like to insert a footnote.
Click "Insert" in the menu bar, and and then point to "Reference" and select "Footnote."
Select the "Number Format" that you desire in the footnotes menu box.
Click "Insert" to place a footnote in the desired area. This will leave a footnote number in the text area you have chosen, and you can then fill in appropriate text from a reference to go along with the footnote number you have added.
Save the document once you have added the footnote number and text.