Zotero offers plugins for word processing programs including Word and LibreOffice. The plugin adds a Zotero toolbar to your word processor that allows you to add citations to your document while you write. This is what the toolbar looks like in Word:
If you want to insert a bibliography using Word, place your cursor at the point in your document where you would like to insert it. Then click the button "Add/Edit Bibliography":
Your bibliography will appear:
Please note: if you have selected a citation style that does not satisfy your particular needs, do not try to change the text in your Word document. If you need to create a new citation style, make a copy of the citation style that is closest to what you want. In Zotero Standalone go to Edit > Preferences > Cite > Style Editor > Save As. Then edit the copy of the style using a text editor (Notepad, TextEditor, etc.). Visit https://www.zotero.org/support/dev/citation_styles/style_editing_step-by-step for detailed instructions.
As you add new in-text citations, your bibliography will grow:
Change citation styles with the "Document Preferences" button:
Here I've changed my citation style from Cell (above) to Science (below):
The toolbar looks different with different operating systems and versions of Word. Mousing over the toolbar will pop up each button's function if they're not clearly labeled.
When installing Zotero Standalone, the toolbar for Word should be automatically installed. If you do not see it, go to http://libanswers.caltech.edu/faq/203919 for more information. And if you need additional citation styles, visit http://libanswers.caltech.edu/faq/203921.