Caution: Automatically-generated bibliographies may contain errors. If you use Zotero to generate a bibliography, you should proofread the bibliography before you submit it to your professor.
It's easy to create a bibliography from your Zotero library.
Select the references or collections you want to include. (To select multiple items, hold the Control key.) Right-click one of the selected items and choose "Create Bibliography." Then, choose the bibliographic style you want, and select the output format.
Or you can just drag and drop references from Zotero into your document! They'll turn into fully formatted citations. This works with any word processor, including Google Docs. You can choose your style (MLA, APA, Chicago, etc.) by going to the Edit menu and selecting "Preferences."
You don't have to open Zotero to create citations. You can create citations within your word processor, while you write, in Google Docs or Microsoft Word or LibreOffice.
Google Docs: The Zotero Connectors for Chrome and Firefox include an add-on for Google Docs. If you've installed the connector, you'll see the Zotero menu in Google Docs. It looks like this:
Note that in order to use this feature, you have to grant Zotero permission to view your Google documents. You also have to have the Zotero app running in the background.
Microsoft Word or LibreOffice: Zotero provides word processor plugins for Word and LibreOffice. The plugins should be automatically installed when you install Zotero, but you can also install the plugins yourself, by going to Zotero's Preferences menu, clicking "Cite," and then clicking "Word Processors."
With the plugins installed, you'll see a new tab. Here's what it looks like in Word:
In order to use this feature, you have to have the Zotero app running in the background.
If you're using a computer that doesn't have Zotero installed, you can generate a bibliography using ZoteroBib.
ZoteroBib is a free service from the makers of Zotero. To cite a source using ZoteroBib, first copy the source's URL (or ISBN or DOI or PMID or arXiv ID or title). Then, go to zbib.org and paste it into the box.
(This GIF is by Dan Stillman. It first appeared here.)
Note that ZoteroBib is only a citation tool, and does not provide the full suite of features that Zotero provides.