​Zotero offers word processing plugins for Word and OpenOffice. The plugin adds a Zotero toolbar to your word processor that allows you to add citations to your document while you write.
To add a citation, click the first button ("Add/Edit Citation") on the toolbar. Search for the reference you want to cite and press Enter. Zotero will add the citation at your cursor.
At the end of your paper, click the "Insert Bibliography" button. Your bibliography will appear, and new citations will be added automatically. Change bibliographic styles with the "Document Preferences" button.
The toolbar looks different on different operating systems and versions of Word. Mousing over the toolbar will pop up each button's function if they're not clearly labeled.
You will need to select your style and other document preferences:
Type an author or title from your Zotero library and select the one for which you intend to insert a citation.
The format and number of a footnote will change as you add or remove footnotes from your document. For instance, if this is the second time you are using the citation in a footnote, the footnote will be the short version. If this footnote ever becomes the first use of that source, it will change to reflect that!