There are 5 main ways to add references to your Zotero library:
You can add references quickly if you already know their ISBN, Digital Object Identifier (DOI), or PubMed ID
1. In the Zotero window click on the Add Item(s) by Identifier button
2. Type or paste the identifier and press enter
You can also manually add items to your Zotero library:
1. In the zotero window, click on the New Item button
2. Select the desired item type from the drop-down menu
3. An empty item of this type will then appear in the center column
4. You can manually enter the item's bibliographic information in the right column
If you have full text PDF files of journal articles, you can often easily retrieve the citation for the articles with a few simple steps.*
First, drag and drop a PDF (or several) into your Zotero library.
Next, right click on the PDF and choose Retrieve Metdata from PDF:
Within seconds, Zotero will convert your imported PDF into a citation and attach the PDF to that citation.
If this is your first attempt at using this feature, you may be prompted to install the PDF indexing plugin. Simply click through the installation prompt and the indexer will install within seconds.
*While this feature can greatly facilitate importing large existing libraries of PDFs, the imported data, especially where Zotero uses Google Scholar, is of lower quality than importing via Web Translator from most scholarly databases.
You can also import items from another reference management software
1. Select "Import..." from the file menu
2. Browse to the file, select it, and click "Open"
3. The items will be imported into your Zotero library in a date-stamped collection
You can use AnyStyle to take references from a Google Doc, Word doc, Google Sheet (etc.) and add them to your Zotero library. It's a great way to add multiple citations to Zotero at once. (Sometimes, the Zotero browser connector is a better option - ask a librarian if you're unsure.)
(Source: Berkley Library Update)
Getting Stuff Into Zotero from zotero on Vimeo.