Adding Items to Your LibraryThere are a few different ways to add citations to your Zotero Library. We'll go through them, from easiest to more time consuming.
Dragging / Dropping PDFsIf you have a PDF on your computer, you can simply drag and drop it into your Zotero Library.
In most cases, Zotero will recognize the article and automatically create a record, pulling in all the relevant citation information. If you drag a PDF into your library and it is not able to pull in the metadata and create a new record, you can right click on the PDF and click on Retrieve Metadata for PDF, which will force Zotero to search for information about the PDF.
In rare cases where Zotero is unable to retrieve metadata for the PDF, you can select Create Parent Item from the right-click menu. This will allow you to enter a unique identifier (like a DOI or PMID number), or you can select Manual Entry -- you'll learn more about these options shortly.
Using the Zotero ConnectorThe easiest way to add a citation to your library is by using Zotero Connector, the browser extension. There are versions available for Chrome, Firefox, Safari, and Edge -- you'll need to download the extension for whichever browser you are using. The browser extension scrapes bibliographic metadata from the web page of a resource and adds it to your library. If the item's listing includes a PDF, Zotero will automatically add that as well. If you need to, you can later edit the entry, but for journal articles and books, it's pretty accurate as-is!
How it works: When you are looking for research (in a database, in the library catalog, on a website, etc.) and you find something you want to add, simply click on the Zotero extension button, and Zotero will import information about this item to your library. The extension button's icon will change depending on what you are looking at.
If you are looking at a journal article, it will look something like this: 
A record for a book looks like this: 
And a website looks like this: 
When you click on the extension, it will automatically add the record to your library, and if it finds a PDF on the page, it will add that as well. By default, it will add it to whatever collection (folder) is highlighted in your library.
Add by Unique IdentifierIf you have unique identifier such as an ISBN, DOI, or PMID number, you can enter it by clicking the Add Item(s) by Identifier button, then hitting the enter button.
Manually Adding CitationsThe most time consuming method is manually adding citations. If you click on the New Item button (the green plus), you can choose an item type. This can be helpful for non-traditional sources, such as white papers, artwork, interviews, or podcasts.
Once you've selected an item type, you can start entering the information into the available fields.
NOTE: If you need to add a White Paper to your Zotero library and are using APA style, you'll need to manually add your citation information. The recommended Item Type to use is Report. Once you've selected this, you will then see a new field for Report Type, where you can manually type the term, White paper. Doing this will ensure that Zotero includes the document type [White paper] in the citation. For example:
Portland Children's Levy. (2020). Many voices, many journeys: Stories from six Portland families [White paper]. https://portlandchildrenslevy.org/report/annual-community-reports
Which Method Should I Use?It is easiest to add research to your Zotero library as you find it.
If you are looking at an article online, use the browser extension
If you see an article in a reference list and there is a DOI number, you can add it using that method
If you have a PDF, dragging and dropping the PDF into your library is easiest