The simplest way to add items to Zotero is to use a Web Browser Connector (install instructions).
When you find a source you would like to save, click on the connector button. You will see a pop-up indicating that Zotero is saving your citation.
If Zotero detects that you're looking at a book or article on a catalog, database, or site, you'll see a book or page icon appear in your browser's address bar. Just click the icon and Zotero will automatically save the citation.
Example1: Adding a book chapter
Example2:Adding a list of items
If you have an item in front of you and you can't find a record for it online, you can create a new citation manually.
First, click on the green plus sign icon and choose the type of source you want to create a citation for from the drop-down menu (additional options are available under "More").
Next, type the bibliographic information in the right panel (Title, author, year of publication,etc..)
If you have a book's ISBN, an online article's DOI or PMID number, just click the magic wand button: "Add item by identifier." Type in the book or article's number, and Zotero will automatically download its information and save it to your library.