Zotero [zoh-TAIR-oh] is a free, easy-to-use tool to help you collect, organize, cite, and share your research sources.
Zotero is an application that can pull source information from the very websites your're using to find resources. You're then able to organize your sources with tags and folders and you can attach PDFs and notes. When you need to reference those sources, Zotero makes it easy to create proper citations and to share sources with friends and colleagues.
Rather watch a video? Zotero.org has a good (if somewhat dated) collection of screencast tutorials.
Navigate to the Zotero download page and select either the Firefox extension or the Standalone. Using Zotero as a Firefox extension requires the user to open Firefox in order to insert citations. The Standalone option is a separate application: it does not live inside an internet browser. For the Standalone, you will want to download the appropriate browser add-on as well (notice that your OS and current browser are automatically detected and highlighted). Installation will follow the typical pattern for your operating system.
Open Zotero by clicking the shortcut icon (Standalone) or by selecting the 'Z' from the menubar in Firefox. You may be prompted to create an account when opening Zotero the first time. Accounts are free, but you are not required to create one. Advantages of creating an account include the ability to sync your Zotero library across multiple computers and the ability to access your library online.
If you choose not to create an account, you may create one later by clicking the 'Actions' icon at the top of the Zotero window, 'Preferences' from the drop-down menu, and then selecting the 'Sync' tab in the new window.