To create a single citation from an item in your Zotero library you right click on the specific item and select Create bibliography from item
From the pane that appears, you select the bibliographic style you want, click on Bibliography, and preferably Copy to clipboard in order to copy and paste your bibliography into your document.
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Then you simply open your word document and paste
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From your library you select the folder that you want to import the bibliography from, and right click to Create bibliography from collection
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Then the steps are repeated (select style, output mode and method) and paste to word document