In Word, change to the EndNote tab and, from the Style drop-down, select Chicago 16th Footnote as the style.
If this style is not showing in the styles list, click on Select Another Style instead, and browse to find Chicago 16th Footnote in the full list of styles, click once to select it, then click the OK button to add it to your list of favourite styles.
Still in Word, place your cursor in the document where you want to add a new citation.
Change to the References tab and add a footnote using Word's footnote function. (Note that this is not an EndNote function.)
Keyboard shortcut on Windows, Ctrl+Alt+F. (On a Mac, Cmmd+Alt+F)
After inserting the footnote, Word will automatically place your cursor in the footnote, ready to add content.
Change to the EndNote 21 tab in Word, and click the Find Citation button (with the magnifying glass). Do not click on the Insert Citation button directly below it - although it is not always clear, they are two separate buttons.
A Find & Insert box will pop up. Type in an author or a word or phrase, or even part of a word, from the citation you wish to use, select the citation in the results list, and click the Insert button (the main part of the button, not the little black arrow at the end).
The appropriate content will be inserted into your footnote, and a reference list will be created (or updated) at the end of the document.
(If you had a 20-page document, the reference list will be at the bottom of page 20. If you had a single paragraph, the reference list will be under the paragraph.)
You might need to add a page number to your citation (often required for quotes).
In Word, click once on the footnote citation to select it. The background will usually turn grey (although this will depend on your Word configuration, it might not change colour).
On the EndNote tab in Word, click on Edit & Manage Citations.
An Edit & Manage Citations box will pop up. Type the page number (or page range) into the Pages field, then click OK.
The page number(s) will be added to your Word citation as appropriate for that type of reference (Chicago has different punctuation for journals and books, for example).