Zotero is available for macOS, Windows, Linux, iOS, and iPadOS. If you're on a Chomebook you can use zBib instead. It's browser-based and should work anywhere.
In addition to Zotero itself, you will need the Zotero connector for whichever browser you use. Connectors are available for Chrome, Safari, Firefox, and Opera.
When you visit a page that Zotero recognizes as a bibliographic item, such as an item in a library database, an icon will appear in your browser's toolbar. The appearance of the icon depends on the type of resource being viewed, with the most common being the book icon and the lined page icon representing a journal article. Some of these items are very difficult to see.
If you're on a web page that Zotero can't identify as a particular type, you'll see a generic page icon. Clicking on this will add a basic entry (often just the URL and the date accessed) for the page to your Zotero library, along with a snapshot of the page.
When you click on the icon, information about the item you are viewing will be automatically entered into your Zotero library.
If you need to add an item for which you have no online record, you can add the item manually using the "new item" button (the green circle with a plus sign), and choosing the type of resource that you want to add.
Once you have selected the appropriate document type, details about the document may be entered in the right-hand panel.
When you save an item to Zotero, look at the data that is being saved. Zotero may have missed something that you need (like the abstract) or recorded data incorrectly (e.g., forenames and surnames mixed up, title in all caps). It's easier to fix mistakes like this when you're collecting the data that it is to go back later when you're trying to put together your bibliography.
Zotero can work with your word processing program (Microsoft Word or OpenOffice) to help you with in-text citations.
Open your Zotero preferences and look at the "Cite" tab to make sure you have the correct add-in for the word processing software you're using. If you're using Zotero for Firefox, you'll need to download the add-ins.
When the add-in is installed, Zotero tools will be available from within your word processor. The appearance of these tools differs based on software versions and platform. The screenshots below show Zotero in Microsoft Word on a Mac.
In Word for Mac, you should see a Zotero tab within Word. The Zotero tools are displayed as icons in this tab. You'll need to have Zotero open to use these tools, even though you'll be working primarily in Word.
Probably the most important tool is "insert citation." This allows you to add in-text citations as you write. When you click this button, you will be presented with a search window where you can search for and select the paper you want to cite. Zotero will then add an in-text citation to the paper. (The first time you use this tool in a given document, you will first be asked to choose a style, then you'll see the search box.)
It is best to add all of your in-text citations with Zotero. Zotero then knows what you have cited, so when you finish your paper you can just click the "Insert Bibliography" button and Zotero will create a reference list consisting only of those items you have cited in-text.