Zotero has the ability to automatically recognize citation information from within library catalogs, electronic databases and many regular web pages. When Zotero recognizes the information on a web page it places a small icon at the end of the location bar. The icons differ depending on what the item is (book, article, newspaper, image etc.).
Zotero also publishes a list of compatible sites, please note that many sites not on the list will automatically work too.