As you browse the web, the Zotero browser tool will be checking to see if there is citation information on a page. If it finds something it can 'grab,' it will indicate this with an icon in the URL bar
If you're looking at a book you'll see this icon: 
If you're looking at a journal article you'll see this icon: 
If you're looking at a newspaper article you'll see this icon: 
Selecting the icon will add the citation to your Zotero library:
If you're looking at multiple citations (for instance, for a page of search results), you'll see this folder icon:
Selecting the folder will bring up a lightbox. Choose whichever results you want to add to your library:
References will be added to whichever folder is highlighted in your Zotero library. They will also appear in your My Library list:
