Two methods for citing sources and creating bibliographies in Zotero:

• For Bibliography -- Left-click or command click on a collection(folder) of citations, choose "Copy to Clipboard" and paste the folder of items into your document.  You may be prompted to select a citation style.

• For Citations within text of a document -- click and hold the item you would like to cite, and drag it into the desired location in your document,  You can add in a page number manually.

With the word processor plugins available for Microsoft Word and LibreOffice you may insert citations through your word processing program--open a document and check for this panel of tools:

• As you add citations, the plugin generates a dynamic bibliography--it updates as you make citation changes in your document! The plug in also allows you to switch the citation style of the entire document.
• The plugin should be automatically installed--you can check on this in your Preferences settings. (More on this and other preference settings on this page.)

Note: Depending on your version of Word and your computer's operating system, the appearance of the plugin tools may vary.

Zotero also compatible with Google Drive documents. The Help page on the Zotero.org website is clear, thorough, and includes images.

For additional information and context, this post from their website may also be of interest.