If you are using Microsoft Word, make use of the built in tools that will help you.
These tools include the following:
In Microsoft Word, go to the 'References' tab. At the end of the sentence / word you wish to reference, simply click on "Insert Footnote" and then type you reference.
To cross-reference, use the 'cross-reference' tool in the captions box. When it asks you what you want to cross-reference to - select 'Footnotes' from the options, and then select the footnote you wish to reference.