Within your document, place your cursor where you want the footnote reference to appear. The select References > Insert Footnote.
Word will automatically generate a line to separate the main body of the document from the footnotes, as well as the reference number. You can then type the citation information.
As you continue to add and delete footnotes, Word will automatically renumber the footnote references for you. If you do not like the default font for the footnotes, you can change it under the Home menu by clicking the arrow in the corner of the Styles options. If using a Mac, click on the Styles Pane icon on the far right of the toolbar.
Look for the Footnote Text (PC)/Footnote Reference (Mac) option within the Styles menu that pops up. If you don't see it, click the Options button (PC) or List: Recommended drop down menu(Mac).
Change the styles menu from Recommended to All styles, then click OK.
Within the Styles menu, find Footnote Text (PC) or Footnote Reference (Mac), click the down arrow to the right of it, and then select Modify from the menu.
Implement your desired changes using the Modify Style pop-up, then click OK. Any footnotes you've already entered into your document will automatically be modified to match the new style parameters you selected.