1. Look for the 
button in the lower right corner of your Firefox browser window. Click on it to open Zotero.
2. Click on the Action icon in Zotero (it looks like a little gear); then choose Preferences:
3. Under the "General" preferences tab, note the options to "Automatically attach associated PDFs" and "Automatically tag items with keywords and subject headings," and click the check boxes for these two settings.
4. Go to the Preferences "Sync" tab. Enter your Zotero user name and password, and check the "sync automatically" check box. This will save the same collections of citations and files that you store on your local computer (in the Firefox profile) on the Zotero server as well. If you use another computer, you can get to your data from the Sync Reset preferences by choosing "Restore from Zotero server," which will erase local data that may have been saved by someone else.
(This feature requires Zotero version 2.0)
It's easy to add PDFs to your Zotero library and automatically import their citation info.
First, enable PDF indexing on the Search tab of Zotero's preferences. Zotero will download and install a small plugin.
Next, just drag your PDF files into the Zotero pane.
Right-click the PDFs and choose "Retrieve Metadata for PDFs." Zotero will retrieve their citation data from Google Scholar and turn them into citeable items with PDF attachments.
If Zotero can't find a match on Google Scholar, don't worry -- you can still save the citation from another catalog or article database, then drag the PDF onto the citation to make it an attachment.
(This feature requires Zotero version 2.0)
Have the book in front of you and want to add it to your Zotero library without having to search for a citation?
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.